Mobile vehicle

ABSTRACT

In a mobile vehicle  1 A having a front wheel  3   f  and a rear wheel  3   r , the steered wheel  3   f  can be steered by an actuator  8 . A control device  15  controls the actuator  8  so as to stabilize the inclination angle φb in the roll direction of the vehicle body  2  and the steering angle δf of the steered wheel  3   f . The control device  15  causes a ratio between the sensitivity of the steering of the steered wheel  3   f  to the change in observed value of the inclination angle φb and the sensitivity of the steering of the steered wheel  3   f  to the change in observed value of the steering angle δf to be changed in accordance with the traveling speed of the mobile vehicle  1 A.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mobile vehicle (mobile object) suchas a two-wheeled vehicle having a front wheel and a rear wheel.

2. Description of the Related Art

In a mobile vehicle, for example a motorcycle, having a front wheel anda rear wheel arranged spaced apart from each other in the longitudinaldirection of the vehicle body, the front wheel usually serves as asteered wheel. In order to enhance the straight traveling property ofthe motorcycle, the steering axis of the front wheel (rotational axis ofsteering of the front wheel) is tilted backward (with a positive casterangle). Further, the axle of the front wheel is arranged on, or slightlybehind, the steering axis.

As a result, a motorcycle of this type usually has a large positivetrail. It should be noted that having a positive trail means that thepoint of intersection of the steering axis and the ground surface withwhich the wheels come into contact lies in front of the ground contactpoint of the steered wheel.

Further, as a motorcycle of this type, a motorcycle which is configuredsuch that the rear wheel is passively steered by a reaction force thatthe rear wheel receives from the road surface when the motorcycle makesa turn is also known, as seen, for example, in Japanese PatentApplication Laid-Open No. 04-224488.

SUMMARY OF THE INVENTION

For two-wheeled vehicles such as motorcycles, it is desired to enhancethe stability of the posture of the vehicle body particularly when thevehicle is stopped or traveling at a low speed.

On the other hand, during a high-speed traveling of the two-wheeledvehicle, the stability of the posture of the vehicle body is higher ascompared to when the vehicle is stopped or traveling at a low speed. Itis therefore desirable that the rider can readily control the posture ofthe vehicle body by, for example, banking the vehicle body in the rolldirection during turning of the two-wheeled vehicle.

In view of the foregoing, it is an object of the present invention toprovide a mobile vehicle which can enhance the stability of the postureof the vehicle body by steering of a front wheel or a rear wheel whenthe vehicle is stopped or traveling at a low speed, and which canfacilitate a rider's control of the posture of the vehicle body when thevehicle is traveling at a high speed.

To achieve the object, the present invention provides a mobile vehiclehaving a vehicle body and a front wheel and a rear wheel arranged spacedapart from each other in a longitudinal direction of the vehicle body,

one of the front wheel and the rear wheel being a steered wheel whichcan be steered about a steering axis tilted backward,

the mobile vehicle including:

a steering actuator which generates a steering force for steering thesteered wheel; and

a control device which controls the steering actuator, wherein

the control device is configured to control the steering actuator so asto stabilize controlled state quantities including a first motionalstate quantity and a second motional state quantity, the first motionalstate quantity being a motional state quantity of an inclination anglein a roll direction of the vehicle body and including at least a valueof the inclination angle, the second motional state quantity being amotional state quantity of a steering angle of the steered wheel andincluding at least a value of the steering angle, and, when a steeringangular acceleration of the steered wheel steered by the steeringactuator or a torque about the steering axis applied to the steeredwheel from the steering actuator is defined as a reference quantity, thecontrol device is configured to control the steering actuator such thata magnitude of a ratio Ra1/Rb1 between sensitivity Ra1 of a change invalue of the reference quantity to a change in observed value of theinclination angle in the roll direction of the vehicle body andsensitivity Rb 1 of a change in value of the reference quantity to achange in observed value of the steering angle of the steered wheelbecomes smaller as a magnitude of an observed value of a traveling speedof the mobile vehicle becomes larger (a first aspect of the invention).

It should be noted that the “first motional state quantity” (motionalstate quantity of the inclination angle in the roll direction of thevehicle body) in the present invention may include a value of theinclination angle alone. Alternatively, it may include, besides thevalue of the inclination angle, a temporal change rate of theinclination angle (inclination angular velocity), for example.

Further, the “second motional state quantity” (motional state quantityof the steering angle of the steered wheel) may include a value of thesteering angle alone. Alternatively, it may include, besides the valueof the steering angle, a temporal change rate of the steering angle(steering angular velocity), for example.

In the mobile vehicle of the first aspect of the invention having thesteered wheel, it has been confirmed, through various experiments andstudies conducted by the present inventors, that steering of the steeredwheel can cause a moment in the roll direction to act on the vehiclebody. Accordingly, the posture state in the roll direction of thevehicle body can be controlled by the steering of the steered wheel.

Therefore, in the first aspect of the invention, the control device usesthe first motional state quantity, including at least a value of theinclination angle in the roll direction (hereinafter, also simplyreferred to as “roll angle”) of the vehicle body, and the secondmotional state quantity, including at least a value of the steeringangle of the steered wheel, as the controlled state quantities, tocontrol the steering actuator so as to stabilize the controlled statequantities.

Here, “to stabilize the controlled state quantities” means to makeactual values of the controlled motional state quantities converge toprescribed desired values, or to generate a moment (in the rolldirection) that acts on the mobile vehicle in the direction of makingthe actual values of the controlled motional state quantities approachthe prescribed desired values, if not sufficient to make them converge.

In this case, the above-described desired value means a value of acontrolled state quantity that is predetermined in correspondence with adesired posture state of the mobile vehicle. Typically adopted for thisdesired value is a value of the controlled state quantity in thestraight-ahead posture state of the mobile vehicle (specifically, thestate where the front wheel and the rear wheel are both standing in theupright posture on the ground surface and the axle centerlines (centersof rotational axes) of the front wheel and the rear wheel extend inparallel with each other in the direction orthogonal to the longitudinaldirection of the vehicle body).

The desired value of a controlled state quantity, however, may be avalue in a posture state other than the straight-ahead posture state ofthe mobile vehicle. For example, in the case where the mobile vehicle isprovided with an operation apparatus for allowing a rider of the mobilevehicle to steer the steered wheel, or in the case where the wheeldifferent from the steered wheel steerable by the aforesaid steeringactuator is a steered wheel not equipped with an actuator for steering,the value may be a desired value (reflecting the requirement of therider) which is determined in accordance with the force applied to theoperation apparatus by the rider's manipulation or the manipulatedvariable of the operation apparatus, or in accordance with the steeringangle of the steered wheel not equipped with the actuator.

In the first aspect of the invention, controlling the steering actuatorso as to stabilize the controlled state quantities as described abovecan basically make the roll angle of the vehicle body and the steeringangle of the steered wheel both converge to, or approach, their desiredvalues.

In the first aspect of the invention, however, the control devicecontrols the steering actuator such that the magnitude of the ratioRa1/Rb1 between the sensitivity Ra1 of the change in value of thereference quantity to the change in observed value of the roll angle ofthe vehicle body and the sensitivity Rb1 of the change in value of thereference quantity to the change in observed value of the steering angleof the steered wheel becomes smaller as the magnitude of the observedvalue of the traveling speed of the mobile vehicle becomes larger.

Therefore, as the magnitude of the observed value of the traveling speedof the mobile vehicle becomes larger (i.e. as the traveling speedbecomes higher), the sensitivity Ra1 of the change in value of thereference quantity to the change in observed value of the roll angle ofthe vehicle body becomes relatively small compared to the sensitivityRb1 of the change in value of the reference quantity to the change inobserved value of the steering angle of the steered wheel.

Consequently, in the case where the traveling speed of the mobilevehicle is in a high-speed range, even if the roll angle of the vehiclebody deviates from the desired value, generation of the driving force ofthe steering actuator for eliminating the divergence is restricted ascompared to when the traveling speed of the mobile vehicle is in alow-speed range.

Accordingly, when a rider is driving the mobile vehicle at a speed in ahigh-speed range, he/she can readily bank the vehicle body of the mobilevehicle for turning.

On the other hand, when the mobile vehicle is stopped or traveling at alow speed, the sensitivity Ra1 of the change in value of the referencequantity to the change in observed value of the roll angle of thevehicle body becomes relatively large compared to the sensitivity Rb1 ofthe change in value of the reference quantity to the change in observedvalue of the steering angle of the steered wheel.

Therefore, when the mobile vehicle is stopped or traveling at a lowspeed, if the roll angle of the vehicle body deviates from the desiredvalue, the generation of the driving force of the steering actuator isperformed for eliminating the divergence actively, as compared to whenthe mobile vehicle is traveling at a speed in a high-speed range. Thisallows the stability of the posture of the vehicle body to be maintainedautonomously, without the need of skillful control by the rider.

Therefore, according to the mobile vehicle of the first aspect of theinvention, it is possible to enhance the stability of the posture of thevehicle body by the steering of a front wheel or a rear wheel when thevehicle is stopped or traveling at a low speed, and also facilitate therider's control of the posture of the vehicle body when the vehicle istraveling at a high speed.

It should be noted that in the first aspect of the invention, the casewhere the magnitude of the aforesaid ratio Ra1/Rb1 becomes smaller asthe magnitude of the observed value of the traveling speed of the mobilevehicle becomes larger may be any of the following: the case where thesensitivity Ra1 becomes smaller as the magnitude of the observed valueof the traveling speed of the mobile vehicle becomes larger; the casewhere the sensitivity Rb1 becomes larger as the magnitude of theobserved value of the traveling speed of the mobile vehicle becomeslarger; the case where the sensitivities Ra1 and Rb1 both become largeras the magnitude of the observed value of the traveling speed of themobile vehicle becomes larger; and the case where the sensitivities Ra1and Rb1 both become smaller as the magnitude of the observed value ofthe traveling speed of the mobile vehicle becomes larger.

In the first aspect of the invention, it is preferable that the firstmotional state quantity included in the controlled state quantities ismade up of a value of the inclination angle in the roll direction of thevehicle body and a temporal change rate of the inclination angle, thatthe second motional state quantity included in the controlled statequantities is made up of a value of the steering angle of the steeredwheel and a temporal change rate of the steering angle, and that thecontrol device is configured to control the steering actuator such thatthe magnitude of the ratio Ra1/Rb1 becomes smaller as the magnitude ofthe observed value of the traveling speed of the mobile vehicle becomeslarger, and also such that the magnitude of a ratio Ra2/Rb2 betweensensitivity Ra2 of the change in value of the reference quantity to thechange in observed value of the temporal change rate of the inclinationangle in the roll direction of the vehicle body and sensitivity Rb2 ofthe change in value of the reference quantity to the change in observedvalue of the temporal change rate of the steering angle of the steeredwheel becomes smaller as the magnitude of the observed value of thetraveling speed of the mobile vehicle becomes larger (a second aspect ofthe invention).

According to the second aspect of the invention, as the magnitude of theobserved value of the traveling speed of the mobile vehicle becomeslarger (i.e. as the traveling speed becomes higher), the sensitivity Ra1of the change in value of the reference quantity to the change inobserved value of the roll angle of the vehicle body becomes relativelysmall compared to the sensitivity Rb1 of the change in value of thereference quantity to the change in observed value of the steering angleof the steered wheel, and additionally, the sensitivity Ra2 of thechange in value of the reference quantity to the change in observedvalue of the temporal change rate (angular velocity) of the roll angleof the vehicle body becomes relatively small compared to the sensitivityRb2 of the change in value of the reference quantity to the change inobserved value of the temporal change rate (angular velocity) of thesteering angle of the steered wheel.

Therefore, in the case where the traveling speed of the mobile vehicleis in a high-speed range, even if the roll angle of the vehicle body andthe temporal change rate thereof deviate from their desired values, thegeneration of the driving force of the steering actuator for eliminatingthe divergences is restricted as compared to when the traveling speed ofthe mobile vehicle is in a low-speed range.

Further, when the mobile vehicle is stopped or traveling at a low speed,if the roll angle of the vehicle body and the temporal change ratethereof deviate from their desired values, the generation of the drivingforce of the steering actuator is performed for eliminating thedivergences actively, as compared to when the traveling speed of themobile vehicle is in a high-speed range.

Therefore, in the case where a rider is driving the mobile vehicle at aspeed in a high-speed range, he/she can more readily bank the vehiclebody of the mobile vehicle for turning. On the other hand, while themobile vehicle is stopped or traveling at a low speed, the stability ofthe posture of the vehicle body can be maintained autonomously, withoutthe need of skillful control by the rider.

It should be noted that in the second aspect of the invention, the casewhere the magnitude of the aforesaid ratio Ra2/Rb2 becomes smaller asthe magnitude of the observed value of the traveling speed of the mobilevehicle becomes larger may be any of the following: the case where thesensitivity Ra2 becomes smaller as the magnitude of the observed valueof the traveling speed of the mobile vehicle becomes larger; the casewhere the sensitivity Rb2 becomes larger as the magnitude of theobserved value of the traveling speed of the mobile vehicle becomeslarger; the case where the sensitivities Ra2 and Rb2 both become largeras the magnitude of the observed value of the traveling speed of themobile vehicle becomes larger; and the case where the sensitivities Ra2and Rb2 both become smaller as the magnitude of the observed value ofthe traveling speed of the mobile vehicle becomes larger.

In the first aspect of the invention, it is preferable that the controldevice is further configured to control the steering actuator such thatthe magnitude of the sensitivity Ra1 of the change in value of thereference quantity to the change in observed value of the inclinationangle in the roll direction of the vehicle body becomes smaller as themagnitude of the observed value of the steering angle of the steeredwheel from a non-steered state thereof becomes larger (a third aspect ofthe invention).

Similarly, in the second aspect of the invention, it is preferable thatthe control device is further configured to control the steeringactuator such that the magnitude of the sensitivity Ra1 of the change invalue of the reference quantity to the change in observed value of theinclination angle in the roll direction of the vehicle body and themagnitude of the sensitivity Ra2 of the change in value of the referencequantity to the change in observed value of the temporal change rate ofthe inclination angle each become smaller as the magnitude of theobserved value of the steering angle of the steered wheel from anon-steered state thereof becomes larger (a fourth aspect of theinvention).

Specifically, in the case where the magnitude of the actual steeringangle of the steered wheel is large, compared to the case where it issmall, the radius of curvature of the ground contact part of the steeredwheel as seen in a cross section including the ground contact point ofthe steered wheel and having a normal direction corresponding to thelongitudinal direction of the vehicle body generally becomes larger.

Therefore, in the case where the magnitude of the actual steering angleof the steered wheel is large, compared to the case where it is small,the change in movement amount of the ground contact point of the steeredwheel according to the change in the steering angle becomes larger.Because of this, the sensitivity of the change in moment in the rolldirection acting on the vehicle body to the change in actual steeringangle of the steered wheel varies in accordance with the actual steeringangle of the steered wheel. Accordingly, if it is configured such thatthe aforesaid sensitivity Ra1, or the sensitivities Ra1 and Ra2, is/areindependent of the actual steering angle, oscillation is likely to occurin the posture control of the vehicle body (control of the roll angle)when the steering angle is relatively large.

In view of the foregoing, in the third aspect of the invention, it hasbeen configured such that the magnitude of the sensitivity Ra1 changesin accordance with the observed value of the steering angle of thesteered wheel, as described above. Similarly, in the fourth aspect ofthe invention, it has been configured such that the magnitudes of thesensitivities Ra1 and Ra2 both change in accordance with the observedvalue of the steering angle of the steered wheel, as described above.This can prevent the above-described oscillation even in the case wherethe actual steering angle of the steered wheel is large. Consequently,it is possible to secure high robustness in the posture control of thevehicle body of the mobile vehicle over a wide steering range of thesteered wheel.

Further, in the first through fourth aspects of the invention, it ispreferable that the mobile vehicle further includes an operationapparatus for a rider riding on the mobile vehicle to hold forperforming steering of the steered wheel, the operation apparatus beingarranged to be rotatively driven by a handlebar actuator for rotativelydriving the operation apparatus in conjunction with the change of thesteering angle of the steered wheel from a non-steered state thereofduring the steering of the steered wheel by the steering actuator, andthat the control device is further configured to control the handlebaractuator such that a rotational amount of the operation apparatus hassaturation characteristics with respect to the steering angle of thesteered wheel from the non-steered state thereof (a fifth aspect of theinvention).

Here, the above-described saturation characteristics refer to thecharacteristics that the sensitivity of the change in rotational amountof the operation apparatus to the change in magnitude of the steeringangle of the steered wheel becomes relatively small when the magnitudeof the steering angle of the steered wheel is large as compared to whenit is small.

According to the fifth aspect of the invention, even if the steeringangle of the steered wheel by the steering actuator becomes relativelylarge, the rotational amount of the operation apparatus is preventedfrom becoming excessively large. This can prevent the rider from havinga sense of discomfort about the movement of the operation apparatus.

It should be noted that in the first through fifth aspects of theinvention described above, the aforesaid control device may adopt, byway of example, the following configuration. The control deviceincludes, for example, an actuator operational target determiningsection which successively receives observed values of the actual valuesof the aforesaid controlled state quantities and determines anoperational target of the aforesaid steering actuator, in accordancewith deviations of the received observed values from desired values ofthe corresponding controlled state quantities for stabilizing thecontrolled state quantities, so as to make the deviations approach zero,by a feedback control law. The control device is configured to controlthe steering actuator in accordance with the determined operationaltarget.

In this case, for the operational target, a desired value of theaforesaid reference quantity, for example, may be adopted.

Supplementally, in the present specification, the “observed value” of agiven state quantity related to the mobile vehicle (such as the rollangle of the vehicle body) means a detected value or an estimate of theactual value of the state quantity. In this case, the “detected value”means an actual value of the state quantity which is detected by anappropriate sensor. The “estimate” means a value which is estimated froma detected value of at least one state quantity having correlation withthe state quantity, on the basis of the correlation, or it means apseudo estimate which can be considered to coincide with, or almostcoincide with, the actual value of the state quantity.

For the “pseudo estimate”, for example in the case where it is expectedthat the actual value of the state quantity can adequately track adesired value of the state quantity, the desired value may be adopted asthe pseudo estimate of the actual value of the state quantity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a mobile vehicle (two-wheeled vehicle)according to a first embodiment of the present invention;

FIG. 2 is a block diagram showing the configuration related to thecontrol of the mobile vehicle according to the first embodiment;

FIG. 3 is a block diagram showing the major functions of the controldevice shown in FIG. 2;

FIG. 4 is a block diagram showing the processing performed by theestimated traveling speed calculating section shown in FIG. 3;

FIG. 5 is a block diagram showing the processing performed by thecontrol gain determining section shown in FIG. 3;

FIG. 6 is a block diagram showing the processing performed by thedesired front-wheel rotational transfer velocity determining sectionshown in FIG. 3;

FIG. 7 is a block diagram showing a first example of the processingperformed by the posture control arithmetic section shown in FIG. 3;

FIG. 8 is a block diagram showing a second example of the processingperformed by the posture control arithmetic section shown in FIG. 3;

FIG. 9 is a block diagram showing a first example of the processingperformed by the desired handlebar angle determining section shown inFIG. 3;

FIG. 10 is a block diagram showing a second example of the processingperformed by the desired handlebar angle determining section shown inFIG. 3;

FIG. 11 is a block diagram showing the processing performed by afront-wheel steering actuator control section included in the controldevice shown in FIG. 2;

FIG. 12 is a block diagram showing the processing performed by afront-wheel driving actuator control section included in the controldevice shown in FIG. 2;

FIG. 13 is a block diagram showing the processing performed by ahandlebar driving actuator control section included in the controldevice shown in FIG. 2;

FIG. 14 is a side view of a mobile vehicle (two-wheeled vehicle)according to a second embodiment of the present invention;

FIG. 15 is a block diagram showing the configuration related to thecontrol of the mobile vehicle according to the second embodiment;

FIG. 16 is a block diagram showing the major functions of the controldevice shown in FIG. 15;

FIG. 17 is a block diagram showing the processing performed by theestimated traveling speed calculating section shown in FIG. 16;

FIG. 18 is a block diagram showing the processing performed by thecontrol gain determining section shown in FIG. 16;

FIG. 19 is a block diagram showing the processing performed by thedesired rear-wheel rotational transfer velocity determining sectionshown in FIG. 16;

FIG. 20 is a block diagram showing an example of the processingperformed by the posture control arithmetic section shown in FIG. 16;

FIG. 21 is a block diagram showing the processing performed by arear-wheel steering actuator control section included in the controldevice shown in FIG. 15;

FIG. 22 is a block diagram showing the processing performed by arear-wheel driving actuator control section included in the controldevice shown in FIG. 15; and

FIG. 23 is a block diagram showing a third example of the processingperformed by the posture control arithmetic section shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

A first embodiment of the present invention will be described below withreference to FIGS. 1 to 13.

Referring to FIG. 1, a mobile vehicle 1A according to the presentembodiment is a two-wheeled vehicle which includes a vehicle body 2, anda front wheel 3 f and a rear wheel 3 r arranged spaced apart from eachother in the longitudinal direction of the vehicle body 2. Hereinafter,the mobile vehicle 1A will be referred to as “two-wheeled vehicle 1A”.

On the upper surface of the vehicle body 2, a seat 6 is provided for arider to sit astride.

At the front portion of the vehicle body 2, a front-wheel supportmechanism 4 for axially supporting the front wheel 3 f, an operationapparatus 7 for a rider who has sat on the seat 6 to hold, and actuators8 and 9 are mounted. The actuator 8 generates a steering force forsteering the front wheel 3 f. The actuator 9 generates a steering forcefor moving the operation apparatus 7 in conjunction with the steering ofthe front wheel 3 f.

The front-wheel support mechanism 4 is made up of a front fork whichincludes a suspension mechanism such as a damper, for example. Themechanical structure of the front-wheel support mechanism is similar tothat of a conventional motorcycle, for example. At one end of thisfront-wheel support mechanism 4 (at its end on the front side of thevehicle body 2), the front wheel 3 f is axially supported, via bearingsor the like, such that it can rotate about the axle centerline(rotational axis of the front wheel 3 f) that extends in the directionorthogonal to the diameter direction of the front wheel 3 f (in thedirection perpendicular to the paper plane of FIG. 1).

In the present embodiment, an actuator 10 for rotatively driving thefront wheel 3 f about its axle centerline is attached to the axle of thefront wheel 3 f. The actuator 10 serves as a power engine whichgenerates a thrust force for the two-wheeled vehicle 1A. In the presentembodiment, this actuator 10 (hereinafter, also referred to as“front-wheel driving actuator 10”) is made up of an electric motor (witha speed reducer).

It should be noted that the actuator 10 may be made up of a hydraulicactuator, for example, instead of the electric motor. Alternatively, theactuator 10 may be made up of an internal combustion engine.Furthermore, the actuator 10 may be attached to the vehicle body 2 at aposition apart from the axle of the front wheel 3 f, and the actuator 10and the axle of the front wheel 3 f may be connected by an appropriatepower transmission device.

The two-wheeled vehicle 1A may be equipped, not with the actuator 10 forrotatively driving the front wheel 3 f about its axle centerline, butwith an actuator for rotatively driving the rear wheel 3 r about itsaxle centerline. Alternatively, the two-wheeled vehicle 1A may beequipped with an actuator for rotatively driving the front wheel 3 f andthe rear wheel 3 r about their respective axle centerlines.

The front-wheel support mechanism 4 is mounted to the front portion ofthe vehicle body 2 such that the mechanism can rotate about a steeringaxis Csf which is tilted backward. This configuration makes the frontwheel 3 f serve as a steered wheel which can be rotated, or, steeredabout the steering axis Csf together with the front-wheel supportmechanism 4. As the steering axis Csf is tilted backward, the frontwheel 3 f has a positive caster angle θcf.

It should be noted that the steering axis Csf being tilted backwardmeans that the steering axis Csf extends obliquely with respect to thelongitudinal direction and up-and-down direction of the vehicle body 2such that the steering axis Csf has its upper portion located rearwardrelative to its lower portion in the front-rear (longitudinal) directionof the vehicle body 2.

Supplementally, in the two-wheeled vehicle 1A of the present embodiment,the relative arrangement of the steering axis Csf and the front wheel 3f in the state where the two-wheeled vehicle 1A is stationary in thestraight-ahead posture (this state will be hereinafter referred to as“basic posture state”) is set, as shown in FIG. 1, such that anintersection point Ef of the steering axis Csf and a straight lineconnecting the center of the axle of the front wheel 3 f and the groundcontact point thereof is located below the ground surface 110 (or, suchthat a height a of the intersection point Ef from the ground surface 110is lower (a<0) than the ground surface 110) in the basic posture state.

In other words, the relative arrangement of the steering axis Csf andthe front wheel 3 f in the above-described basic posture state is setsuch that the point of intersection of the steering axis Csf and theground surface 110 is located behind the ground contact point of thefront wheel 3 f (such that the front wheel 3 f has a negative trail) inthe basic posture state.

It should be noted that the basic posture state of the two-wheeledvehicle 1A more specifically refers to the state where the front wheel 3f and the rear wheel 3 r are both stationary in the upright posture incontact with the ground surface 110 and the axle centerlines (centers ofthe rotational axes) of the front wheel 3 f and the rear wheel 3 rextend in parallel with each other in the direction orthogonal to thelongitudinal direction of the vehicle body 2.

In the two-wheeled vehicle 1A according to the present embodiment, therelative arrangement of the steering axis Csf and the front wheel 3 f inthe basic posture state is set, as stated above, such that the height aof the intersection point Ef from the ground surface 110 is lower thanthe ground surface 110, for the following reason.

According to various experiments and studies conducted by the presentinventors, in order to cause a moment (in the roll direction) effectivein stably controlling the posture of the vehicle body 2 to act on thevehicle body 2 by the steering of the front wheel 3 f of the two-wheeledvehicle 1A, it is preferable that the height a of the aforesaidintersection point Ef from the ground surface 110 is lower than acertain level (including the case where it is lower than the groundsurface 110).

In view of the foregoing, in the present embodiment, the relativearrangement of the steering axis Csf and the front wheel 3 f in thebasic posture state has been set as described above, by way of example,such that the front wheel 3 f of the two-wheeled vehicle 1A has anegative trail. The trail of the front wheel 3 f, however, does notnecessarily have to be negative; the relative arrangement of thesteering axis Csf and the front wheel 3 f may be set such that the frontwheel 3 f has a positive trail. Basically, what is required is only thatthe steering of the front wheel 3 f can cause a moment in the rolldirection to act on the vehicle body 2.

The aforesaid actuator 8 generates, as a steering force for performingthe steering of the front wheel 3 f, a rotative driving force to causethe front wheel 3 f to rotate about the steering axis Csf. In thepresent embodiment, this actuator 8 is made up of an electric motor(with a speed reducer). The actuator 8 (hereinafter, also referred to as“front-wheel steering actuator 8”) is connected to the front-wheelsupport mechanism 4 so as to apply the rotative driving force about thesteering axis Csf to the front-wheel support mechanism 4.

Accordingly, as the rotative driving force is applied from thefront-wheel steering actuator 8 to the front-wheel support mechanism 4,the front-wheel support mechanism 4 is rotatively driven about thesteering axis Csf together with the front wheel 3 f. As a result, thefront wheel 3 f is steered by the rotative driving force from thefront-wheel steering actuator 8.

It should be noted that the actuator 8 is not limited to the electricmotor; it may be made up, for example, of a hydraulic actuator.

The operation apparatus 7 is mounted to the front portion of the vehiclebody 2 such that the operation apparatus 7 can rotate about a handlebaraxis Ch which is parallel to the steering axis Csf of the front wheel 3f. Although not shown in detail in the figure, this operation apparatus7 is equipped with an accelerator grip, brake lever, turn signal switch,and so on, as with the handlebar of a conventional motorcycle.

The aforesaid actuator 9 generates, as a steering force for moving theoperation apparatus 7, a rotative driving force for causing theoperation apparatus 7 to rotate about the handlebar axis Ch. In thepresent embodiment, this actuator 9 is made up of an electric motor(with a speed reducer). The actuator 9 (hereinafter, also referred to as“handlebar driving actuator 9”) is connected to the operation apparatus7 so as to apply the rotative driving force about the handlebar axis Chto the operation apparatus 7.

In the two-wheeled vehicle 1A of the present embodiment, as shown inFIG. 1, the handlebar axis Ch of the operation apparatus 7 is offsetfrom the steering axis Csf of the front wheel 3 f. Alternatively, thehandlebar axis Ch may be arranged concentrically with the steering axisCsf. Still alternatively, the handlebar axis Ch may be tilted withrespect to the steering axis Csf.

Further, the actuator 9 may be made up of a hydraulic actuator, forexample, instead of the electric motor.

At the rear portion of the vehicle body 2, a rear-wheel supportmechanism 5 for axially supporting the rear wheel 3 r in a rotatablemanner is mounted. The rear-wheel support mechanism 5 includes a swingarm 11, and a suspension mechanism 12 made up of a coil spring, damper,and so on. These mechanical structures are similar to those in therear-wheel support mechanism in a conventional motorcycle, for example.

At one end of the swing arm 11 (at its end on the rear side of thevehicle body 2), the rear wheel 3 r is axially supported, via bearingsor the like, such that it can rotate about the axle centerline (centerof the rotational axis of the rear wheel 3 r) that extends in thedirection orthogonal to the diameter direction of the rear wheel 3 r (inthe direction perpendicular to the paper plane of FIG. 1). It should benoted that the rear wheel 3 r is a non-steered wheel.

Besides the above-described mechanical configuration, the two-wheeledvehicle 1A includes, as shown in FIG. 2, a control device 15 whichcarries out control processing for controlling the operations of theaforesaid front-wheel steering actuator 8, handlebar driving actuator 9,and front-wheel driving actuator 10 (and, hence, controlling the postureof the vehicle body 2 and so on).

The two-wheeled vehicle 1A further includes, as sensors for detectingvarious kinds of state quantities necessary for the control processingin the control device 15, a vehicle-body inclination detector 16 fordetecting an inclination angle φb in the roll direction of the vehiclebody 2, a front-wheel steering angle detector 17 for detecting asteering angle δf (angle of rotation about the steering axis Csf) of thefront wheel 3 f, a handlebar angle detector 18 for detecting a handlebarangle δh which is the rotational angle (angle of rotation about thehandlebar axis Ch) of the operation apparatus 7, a handlebar torquedetector 19 for detecting a handlebar torque Th which is the torqueacting on the operation apparatus 7 about the handlebar axis Ch, afront-wheel rotational speed detector 20 for detecting a rotationalspeed (angular velocity) of the front wheel 3 f, and an acceleratormanipulation detector 21 which outputs a detection signal correspondingto the accelerator manipulated variable which is the manipulatedvariable (rotational amount) of the accelerator grip of the operationapparatus 7.

It should be noted that the steering angle δf of the front wheel 3 fmore specifically means the rotational angle of the front wheel 3 f fromthe steering angle (neutral steering angle) in its non-steered state(the state in which the direction of the axle centerline of the frontwheel 3 f is orthogonal to the longitudinal direction of the vehiclebody 2). Therefore, the steering angle δf of the front wheel 3 f in thenon-steered state is “0”. The positive rotational direction of thesteering angle δf of the front wheel 3 f corresponds to the direction ofrotation that makes the front end of the front wheel 3 f turn left withrespect to the vehicle body 2 (in other words, the direction in whichthe front wheel 3 f turns counterclockwise about the steering axis Csfas the two-wheeled vehicle 1A is seen from above).

Further, the handlebar angle δh of the operation apparatus 7 means therotational angle of the operation apparatus 7 from its posture statecorresponding to the non-steered state of the front wheel 3 f. Thepositive rotational direction of the handlebar angle δh corresponds tothe direction in which the operation apparatus 7 turns counterclockwiseabout the handlebar axis Ch as the two-wheeled vehicle 1A is seen fromabove.

The control device 15, which is an electronic circuit unit made up of aCPU, RAM, ROM, interface circuit and so on, is mounted on the vehiclebody 2. This control device 15 is configured to receive outputs(detection signals) from the respective detectors 16 to 21 describedabove.

The control device 15 may include a plurality of CPUs or processors.Further, the control device 15 may be made up of a plurality of mutuallycommunicable electronic circuit units.

The vehicle-body inclination detector 16, which is made up of anacceleration sensor and a gyro sensor (angular velocity sensor), forexample, is mounted on the vehicle body 2. In this case, the controldevice 15 carries out arithmetic processing on the basis of the outputsof the acceleration sensor and the gyro sensor, to measure theinclination angle in the roll direction (more specifically, theinclination angle in the roll direction with respect to the verticaldirection (direction of gravitational force)) of the vehicle body 2. Forthis measurement, the technique proposed by the present applicant inJapanese Patent No. 4181113, for example, may be adopted.

The front-wheel steering angle detector 17 is made up, for example, of arotary encoder attached to the front-wheel steering actuator 8 (electricmotor) on the aforesaid steering axis Csf.

The handlebar angle detector 18 is made up, for example, of a rotaryencoder attached to the handlebar driving actuator 9 (electric motor) onthe aforesaid handlebar axis Ch.

The handlebar torque detector 19 is made up, for example, of a forcesensor interposed between the operation apparatus 7 and the handlebardriving actuator 9.

The front-wheel rotational speed detector 20 is made up, for example, ofa rotary encoder attached to the axle of the front wheel 3 f.

The accelerator manipulation detector 21 is made up, for example, of arotary encoder or a potentiometer built in the operation apparatus 7.

The functions of the above-described control device 15 will be describedfurther with reference to FIG. 3. The XYZ coordinate system used in thefollowing description is, as shown in FIG. 1, a coordinate system inwhich, in the basic posture state of the two-wheeled vehicle 1A, thevertical direction (up-and-down direction) is defined as the Z-axisdirection, the longitudinal direction of the vehicle body 2 as theX-axis direction, the lateral direction of the vehicle body 2 as theY-axis direction (Y-axis not shown in the figure), and a point on theground surface 110 immediately beneath the overall center of gravity Gof the two-wheeled vehicle 1A as the origin.

Further, in the following description, the suffix “_act” is added to thereference characters of a state quantity as a sign indicating an actualvalue or its observed value (detected value or estimate). For a desiredvalue, the suffix “_cmd” is added.

The control device 15 includes, as functions implemented when the CPUexecutes installed programs (functions implemented by software) or asfunctions implemented by hardware, as shown in FIG. 3: an estimatedtraveling speed calculating section 33 which calculates an estimate ofthe actual value Vox_act (hereinafter, referred to as “estimatedtraveling speed Vox_act”) of the traveling speed Vox of the two-wheeledvehicle 1A, a desired posture state determining section 34 whichdetermines a desired value φb_cmd (hereinafter, referred to as “desiredroll angle φb_cmd”) of the roll angle (inclination angle in thedirection about the X axis (roll direction)) φb of the vehicle body 2and a desired value φb_dot_cmd (hereinafter, referred to as “desiredroll angular velocity φb_dot_cmd”) of the roll angular velocity φb_dotwhich is a temporal change rate of the roll angle φb, a control gaindetermining section 35 which determines values of a plurality of gainsK1, K2, K3, K4, and Kh for posture control of the vehicle body 2, and adesired front-wheel rotational transfer velocity determining section 36which determines a desired value Vf_cmd (hereinafter, referred to as“desired front-wheel rotational transfer velocity Vf_cmd”) of therotational transfer velocity Vf of the front wheel 3 f (translationalvelocity of the front wheel 3 f as the front wheel 3 f rolls on theground surface 110).

The control device 15 further includes: a posture control arithmeticsection 37 which carries out arithmetic processing for the posturecontrol of the vehicle body 2 to thereby determine a desired valueδf_cmd (hereinafter, referred to as “desired front-wheel steering angleδf_cmd”) of the steering angle δf of the front wheel 3 f, a desiredvalue δf_dot_cmd (hereinafter, referred to as “desired front-wheelsteering angular velocity δf_dot_cmd”) of the steering angular velocityδf_dot which is a temporal change rate of the steering angle δf, and adesired value δf_dot2_cmd (hereinafter, referred to as “desiredfront-wheel steering angular acceleration δf_dot2_cmd”) of the steeringangular acceleration δf_dot2 which is a temporal change rate of thesteering angular velocity δf_dot, and a desired handlebar angledetermining section 38 which determines a desired value δh_cmd(hereinafter, referred to as “desired handlebar angle δh_cmd”) of thehandlebar angle δh of the operation apparatus 7, and a desired valueδh_dot_cmd (hereinafter, referred to as “desired handlebar angularvelocity δh_dot_cmd”) of the handlebar angular velocity δh_dot which isa temporal change rate of the handlebar angle δh.

The control device 15 carries out the processing in the above-describedfunctional sections successively at prescribed control processingcycles. The control device 15 then controls the front-wheel steeringactuator 8 in accordance with the desired front-wheel steering angleδf_cmd, the desired front-wheel steering angular velocity δf_dot_cmd,and the desired front-wheel steering angular acceleration δf_dot2_cmddetermined by the posture control arithmetic section 37.

Further, the control device 15 controls the front-wheel driving actuator10 in accordance with the desired front-wheel rotational transfervelocity Vf_cmd determined by the desired front-wheel rotationaltransfer velocity determining section 36.

Further, the control device 15 controls the handlebar driving actuator 9in accordance with the desired handlebar angle δh_cmd and the desiredhandlebar angular velocity δh_dot_cmd determined by the desiredhandlebar angle determining section 38.

The control processing performed by the control device 15 will bedescribed below in detail.

At each control processing cycle, the control device 15 first carriesout the processing in the estimated traveling speed calculating section33.

As shown in FIG. 3, the estimated traveling speed calculating section 33receives an estimate of the actual value Vf_act (hereinafter, referredto as “estimated front-wheel rotational transfer velocity Vf_act”) ofthe rotational transfer velocity Vf of the front wheel 3 f(translational velocity of the front wheel 3 f as the front wheel 3 frolls on the ground surface 110), and a detected value of the actualvalue δf_act (hereinafter, referred to as “detected front-wheel steeringangle δf_act”) of the steering angle δf of the front wheel 3 f, which isindicated by an output from the front-wheel steering angle detector 17.

It should be noted that the estimated front-wheel rotational transfervelocity Vf_act is a velocity which is calculated by multiplying adetected value (observed value) of the rotational angular velocity ofthe front wheel 3 f, indicated by an output from the aforesaidfront-wheel rotational speed detector 20, by a predetermined effectiverolling radius of the front wheel 3 f.

The estimated traveling speed calculating section 33 carries out theprocessing shown in the block diagram in FIG. 4 to calculate anestimated traveling speed Vox_act.

In FIG. 4, a processing section 33-1 is a processing section whichmultiplies a detected front-wheel steering angle δf_act at the currenttime by a cosine value cos(θcf) of the caster angle θcf of the frontwheel 3 f, to thereby calculate an estimate of the actual value δ′f_act(hereinafter, referred to as “estimated front-wheel effective steeringangle δ′f_act”) of a front-wheel effective steering angle δ′f whichcorresponds to the rotational angle in the yaw direction of the frontwheel 3 f.

Here, the front-wheel effective steering angle δ′f is an angle of theline of intersection of the ground surface 110 and the rotational planeof the front wheel 3 f being steered (plane passing through the centerof the axle of the front wheel 3 f and orthogonal to the axle centerlineof the front wheel 3 f) with respect to the longitudinal direction(X-axis direction) of the vehicle body 2.

In the case where the roll angle φb of the vehicle body 2 is relativelysmall, the estimated front-wheel effective steering angle δ′f_act can becalculated approximately by the following expression (1). The processingin the above-described processing section 33-1 is the processing ofapproximately calculating δ′f_act by the expression (1).

δ′f_act=cos(θcf)*δf_act  (1)

To further improve the accuracy of δ′f_act, δ′f_act may be obtained by amapping from δf_act. Alternatively, to still further improve theaccuracy of δ′f_act, δf_act may be obtained by a mapping(two-dimensional mapping) or the like from the detected front-wheelsteering angle δf_act and a detected value of the actual roll angleφb_act of the vehicle body 2, which is indicated by an output from thevehicle-body inclination detector 16.

In FIG. 4, a processing section 33-2 represents a processing sectionwhich obtains a cosine value cos(δ′f_act) of the estimated front-wheeleffective steering angle δ′f_act calculated in the processing section33-1, and a processing section 33-3 represents a processing sectionwhich multiplies an estimated front-wheel rotational transfer velocityVf_act at the current time by the above-described cosine valuecos(δ′f_act) to thereby calculate an estimated traveling speed Vox_act.

Accordingly, the estimated traveling speed calculating section 33 isconfigured to calculate Vox_act by multiplying Vf_act by the cosinevalue cos(δ′f_act) of δ′f_act. That is, Vox_act is calculated by thefollowing expression (2).

$\begin{matrix}\begin{matrix}{{Vox\_ act} = {{Vf\_ act}*{\cos \left( {\delta^{\prime}{f\_ act}} \right)}}} \\{= {{Vf\_ act}*{\cos \left( {{\delta f\_ act}*{\cos \left( {\theta \; {cf}} \right)}} \right)}}}\end{matrix} & (2)\end{matrix}$

The estimated traveling speed Vox_act calculated in this mannercorresponds to a component in the X-axis direction of the estimatedfront-wheel rotational transfer velocity Vf_act.

It should be noted that in the processing in the estimated travelingspeed calculating section 33, instead of the detected front-wheelsteering angle δf_act and the estimated front-wheel rotational transfervelocity Vf_act at the current time, a value (last time's value)δf_cmd_p of the desired front-wheel steering angle δf_cmd, calculated bythe posture control arithmetic section 37 (described later) in the lasttime's control processing cycle, and a value (last time's value)Vf_cmd_p of the desired front-wheel rotational transfer velocity Vf_cmd,calculated by the desired front-wheel rotational transfer velocitydetermining section 36 (described later) in the last time's controlprocessing cycle, respectively, may be used. More specifically, δf_cmd_pand Vf_cmd_p may be used to perform computation similar to that in theright side of the above expression (2), and the resultant value(=Vf_cmd_p*cos(δf_cmd_p*cos(θcf))) may be obtained as a pseudo estimate(alternative observed value) as an alternative to the estimatedtraveling speed Vox_act.

Alternatively, in obtaining the pseudo estimate (alternative observedvalue) as an alternative to the estimated traveling speed Vox_act,δf_cmd_p may be used instead of the detected front-wheel steering angleδf_act at the current time, and the estimated front-wheel rotationaltransfer velocity Vf_act may be used as it is. Conversely, Vf_cmd_p maybe used instead of the estimated front-wheel rotational transfervelocity Vf_act at the current time, and the detected front-wheelsteering angle δf_act may be used as it is.

Still alternatively, an observed value of the actual rotational angularvelocity of the rear wheel 3 r (detected by an appropriate detector suchas a rotary encoder) may be multiplied by a predetermined effectiverolling radius of the rear wheel 3 r to estimate an actual rotationaltransfer velocity of the rear wheel 3 r, and the resultant estimate maybe obtained as the estimated traveling speed Vox_act.

Next, the control device 15 carries out the processing in the desiredfront-wheel rotational transfer velocity determining section 36.

As shown in FIG. 3, the desired front-wheel rotational transfer velocitydetermining section 36 receives a detected value of the actual value ofthe accelerator manipulated variable, which is indicated by an outputfrom the aforesaid accelerator manipulation detector 21.

The desired front-wheel rotational transfer velocity determining section36 determines a desired front-wheel rotational transfer velocity Vf_cmdby the processing shown in the block diagram in FIG. 6, i.e. theprocessing in a processing section 36-1.

The processing section 36-1 determines the desired front-wheelrotational transfer velocity Vf_cmd from a detected value of theaccelerator manipulated variable at the current time, by a presetconversion function.

The conversion function is a function which is defined, for example, bya mapping or an arithmetic expression. This conversion function isbasically set such that Vf_cmd determined by the conversion functionincreases monotonically as the accelerator manipulated variableincreases.

The conversion function is set, for example, with the trend asillustrated by the graph in FIG. 6. In this case, the processing section36-1 determines Vf_cmd to be zero when the detected value of theaccelerator manipulated variable falls within the dead band range (rangenear zero) from zero to a prescribed first accelerator manipulatedvariable A1.

Further, when the detected value of the accelerator manipulated variablefalls within the range from the first accelerator manipulated variableA1 to a prescribed second accelerator manipulated variable A2 (>A1), theprocessing section 36-1 determines Vf_cmd such that Vf_cmd increasesmonotonically as the accelerator manipulated variable increases and thatthe rate of increase of Vf_cmd (increase of Vf_cmd per unit increase ofthe accelerator manipulated variable) increases smoothly.

When the detected value of the accelerator manipulated variable fallswithin the range from the second accelerator manipulated variable A2 toa prescribed third accelerator manipulated variable A3 (>A2), theprocessing section 36-1 determines Vf_cmd such that Vf_cmd increasesmonotonically, at a constant rate of increase, as the acceleratormanipulated variable increases.

Further, when the detected value of the accelerator manipulated variableexceeds the third accelerator manipulated variable A3, the processingsection 36-1 determines Vf_cmd such that it remains at a constant value(at the value corresponding to A3).

Next, the control device 15 carries out the processing in the controlgain determining section 35. As shown in FIG. 3, the control gaindetermining section 35 receives, via a delay element 39, a last time'sdesired front-wheel steering angle δf_cmd_p, which is a value (lasttime's value) of the desired front-wheel steering angle δf_cmddetermined by the posture control arithmetic section 37 in the lasttime's control processing cycle of the control device 15. The controlgain determining section 35 also receives an estimated traveling speedVox_act calculated by the estimated traveling speed calculating section33 in the current time's control processing cycle.

The control gain determining section 35 carries out the processing shownin the block diagram in FIG. 5, for example, to determine values of aplurality of gains K1, K2, K3, K4, and Kh for the posture control of thevehicle body 2.

The values of the gains K1, K2, K3, K4, and Kh are each determinedvariably in accordance with δf_cmd_p and Vox_act, or in accordance withVox_act, as will be described in detail later.

Next, the control device 15 carries out the processing in the desiredposture state determining section 34. The desired posture statedetermining section 34 determines a desired roll angle φb_cmd and adesired roll angular velocity φb_dot_cmd of the vehicle body 2. In thepresent embodiment, the desired posture state determining section 34sets both of the desired roll angle φb_cmd and the desired roll angularvelocity φb_dot_cmd to zero, by way of example.

Next, the control device 15 carries out the processing in the posturecontrol arithmetic section 37. As shown in FIG. 3, the posture controlarithmetic section 37 receives the desired roll angle φb_cmd and thedesired roll angular velocity φb_dot_cmd determined by the desiredposture state determining section 34, a detected value φb_act(hereinafter, referred to as “detected roll angle φb_act”) of the actualroll angle and a detected value φb_dot_act (hereinafter, referred to as“detected roll angular velocity φb_dot_act”) of the actual roll angularvelocity, indicated by an output from the vehicle-body inclinationdetector 16, the gains K1, K2, K3, K4, and Kh determined by the controlgain determining section 35, and a detected value Th_act (hereinafter,referred to as “detected handlebar torque Th_act”) of the actual valueof the handlebar torque Th, indicated by an output from the aforesaidhandlebar torque detector 19.

The posture control arithmetic section 37 uses the above-described inputvalues to carry out the processing shown in the block diagram in FIG. 7,to thereby determine a desired front-wheel steering angle δf_cmd, adesired front-wheel steering angular velocity δf_dot_cmd, and a desiredfront-wheel steering angular acceleration δf_dot2_cmd.

In FIG. 7, a processing section 37-1 represents a processing sectionwhich multiplies Th_act by the gain Kh to convert Th_act into a requiredvalue of the angular acceleration of the steering angle of the frontwheel 3 f, a processing section 37-2 represents a processing sectionwhich obtains a deviation of a detected roll angle φb_act from a desiredroll angle φb_cmd, a processing section 37-3 represents a processingsection which multiplies the output of the processing section 37-2 bythe gain K1, a processing section 37-4 represents a processing sectionwhich obtains a deviation of a detected roll angular velocity φb_dot_actfrom a desired roll angular velocity φb_dot_cmd, a processing section37-5 represents a processing section which multiplies the output of theprocessing section 37-4 by the gain K2, a processing section 37-6represents a processing section which multiplies a last time's desiredfront-wheel steering angle δf_cmd_p by the gain K3, a processing section37-7 represents a processing section which multiplies a last time'sdesired front-wheel steering angular velocity δf_dot_cmd_p, which is avalue of the desired front-wheel steering angular velocity δf_dot_cmddetermined by the posture control arithmetic section 37 in the lasttime's control processing cycle, by the gain K4, a processing section37-8 represents a processing section which calculates a sum of theoutputs from the processing sections 37-3 and 37-5 and the values, eachmultiplied by −1, of the outputs from the processing sections 37-6 and37-7, and a processing section 37-9 represents a processing sectionwhich sums up the outputs from the processing sections 37-8 and 37-1 tothereby calculate a desired front-wheel steering angular accelerationδf_dot2_cmd.

Further, a processing section 37-10 represents a processing sectionwhich integrates the output of the processing section 37-9 to obtain adesired front-wheel steering angular velocity δf_dot_cmd, a processingsection 37-11 represents a delay element which outputs the output fromthe processing section 37-10 in the last time's control processing cycle(i.e. last time's desired front-wheel steering angular velocityδf_dot_cmd_p) to the processing section 37-7, a processing section 37-12represents a processing section which integrates the output of theprocessing section 37-10 to obtain a desired front-wheel steering angleδf_cmd, and a processing section 37-13 represents a delay element whichoutputs the output from the processing section 37-12 in the last time'scontrol processing cycle (i.e. last time's desired front-wheel steeringangle δf_cmd_p) to the processing section 37-6.

Accordingly, the posture control arithmetic section 37 calculates thedesired front-wheel steering angular acceleration δf_dot2_cmd by thefollowing expression (3).

$\begin{matrix}{{{\delta f\_ dot2}{\_ cmd}} = {\left( {{K\; 1*\left( {{\varphi b\_ cmd} - {\varphi b\_ act}} \right)} + {K\; 2*\left( {{{\varphi b\_ dot}{\_ cmd}} - {{\varphi b\_ dot}{\_ act}}} \right)} + {K\; 3*{\delta f\_ cmd}{\_ p}} - {K\; 4*{\delta f\_ dot}{\_ cmd}{\_ p}}} \right) + {{Kh}*{Th\_ act}}}} & (3)\end{matrix}$

In the above expression (3), K1*(φb_cmd−φb_act) is a feedbackmanipulated variable having the function of making the deviation(φb_cmd−φb_act) approach “0”, K2*(φb_dot_cmd−φb_dot_act) is a feedbackmanipulated variable having the function of making the deviation(φb_dot_cmd−φb_dot_act) approach “0”, −K3*δf_cmd_p is a feedbackmanipulated variable having the function of making δf_cmd approach “0”,and −K4*δf_dot_cmd_p is a feedback manipulated variable having thefunction of making δf_dot_cmd approach “0”.

Further, Kh*Th_act is a feedforward manipulated variable correspondingto the actual handlebar torque (detected handlebar torque Th_act)applied to the operation apparatus 7 by the rider.

The posture control arithmetic section 37 integrates δf_dot2_cmddetermined by the above expression (3) to determine a desiredfront-wheel steering angular velocity δf_dot_cmd. Further, the posturecontrol arithmetic section 37 integrates this δf_dot_cmd to determine adesired front-wheel steering angle δf_cmd.

It should be noted that δf_cmd_p and δf_dot_cmd_p used in thecomputation of the expression (3) have the meanings as pseudo estimates(alternative observed values) of the actual steering angle and steeringangular velocity, respectively, of the front wheel 3 f at the currenttime. Therefore, instead of δf_cmd_p, a detected front-wheel steeringangle δf_act at the current time may be used. Further, instead ofδf_dot_cmd_p, a detected front-wheel steering angular velocityδf_dot_act (detected value of the actual steering angular velocity ofthe front wheel 3 f) based on an output from the aforesaid front-wheelsteering angle detector 17 may be used.

The above has described the processing in the posture control arithmeticsection 37.

In accordance with the processing in the posture control arithmeticsection 37, the desired front-wheel steering angular accelerationδf_dot2_cmd is basically determined, in the case where no handlebartorque Th is applied to the operation apparatus 7, such that anydivergence of the actual roll angle (detected roll angle φb_act) of thevehicle body 2 of the two-wheeled vehicle 1A from a desired roll angleφb_cmd, or any divergence of the actual roll angular velocity (detectedroll angular velocity φb_dot_act) of the vehicle body 2 of thetwo-wheeled vehicle 1A from a desired roll angular velocity φb_dot_cmd,is eliminated through manipulation of the steering angle δf of the frontwheel 3 f (and, hence, that the actual roll angle or roll angularvelocity of the vehicle body 2 of the two-wheeled vehicle 1A is restoredto the desired roll angle or desired roll angular velocity).

Further, in the present embodiment, the desired front-wheel steeringangle δf_cmd and the desired front-wheel steering angular velocityδf_dot_cmd are both “0”. Therefore, in the state where the actual rollangle of the vehicle body 2 of the two-wheeled vehicle 1A is held at avalue which coincides, or almost coincides, with the desired roll angleφb_cmd, the desired front-wheel steering angular accelerationδf_dot2_cmd is determined so as to keep the actual steering angle of thefront wheel 3 f at “0” or almost “0”.

Furthermore, in the case where a handlebar torque Th is applied to theoperation apparatus 7, a feedforward manipulated variable correspondingto the detected handlebar torque Th_act is added to the desiredfront-wheel steering angular acceleration δf_dot2_cmd.

It should be noted that, instead of adding the feedforward manipulatedvariable corresponding to the detected handlebar torque Th_act toδf_dot2_cmd as described above, it may be configured to add thefeedforward manipulated variable corresponding to the detected handlebartorque Th_act (value obtained by multiplying Th_act by a gain) to thedesired front-wheel steering angular velocity δf_dot_cmd or to thedesired front-wheel steering angle δf_cmd.

Alternatively, instead of adding the feedforward manipulated variablecorresponding to the detected handlebar torque Th_act to δf_dot2_cmd, itmay be configured to correct the desired roll angle φb_cmd in accordancewith Th_act and to use the corrected desired roll angle instead ofφb_cmd, as shown, for example, in the block diagram in FIG. 8.

In the processing in the posture control arithmetic section 37 shown inthe block diagram in FIG. 8, a processing section 37-14 is providedinstead of the processing section 37-9 shown in FIG. 7. The processingsection 37-14 subtracts the output (=Kh*Th_act) of the processingsection 37-1 from the desired roll angle φb_cmd to correct φb_cmd. Itshould be noted that the value of the gain Kh by which Th_act ismultiplied in this case is usually different from the value of the gainKh used in the processing section 37-1 in the block diagram in FIG. 7.

The processing section 37-14 then supplies the corrected desired rollangle (=φb_cmd−Kh*Th_act) to the processing section 37-2, instead ofφb_cmd.

Further, in the processing in the block diagram in FIG. 8, the outputfrom the processing section 37-8, as it is, is determined to be adesired front-wheel steering angular acceleration δf_dot2_cmd, and issupplied to the processing section 37-10.

In other respects, the processing shown in the block diagram in FIG. 8is identical to that shown in FIG. 7.

Accordingly, in the processing in the posture control arithmetic section37 shown in FIG. 8, the desired front-wheel steering angularacceleration δf_dot2_cmd is calculated by the following expression (4).

$\begin{matrix}{{{\delta f\_ dot2}{\_ cmd}} = {{K\; 1*\left( {\left( {{\varphi b\_ cmd} - {{Kh}*{Th\_ act}}} \right) - {\varphi b\_ act}} \right)} + {K\; 2*\left( {{{\varphi b\_ dot}{\_ cmd}} - {{\varphi b\_ dot}{\_ act}}} \right)} - {K\; 3*{\delta f\_ cmd}{\_ p}} - {K\; 4*{\delta f\_ dot}{\_ cmd}{\_ p}}}} & (4)\end{matrix}$

When the value of the gain Kh used in the processing section 37-1 in theblock diagram in FIG. 7 is divided by the gain K1 and the obtained valueis multiplied by −1, and when the resultant value is used as the gain Khin the processing section 37-1 in the block diagram in FIG. 8, then theblock diagram in FIG. 8 becomes equivalent to the block diagram in FIG.7.

In the block diagram in FIG. 7 or the block diagram in FIG. 8, a valueobtained by multiplying the detected handlebar torque Th_act by aprescribed gain may be added to the output of the processing section37-10.

Alternatively, in the block diagram in FIG. 7 or the block diagram inFIG. 8, a value obtained by multiplying the detected handlebar torqueTh_act by a prescribed gain may be added to the output of the processingsection 37-12.

Still alternatively, instead of the detected handlebar torque Th_act asit is, the detected handlebar torque Th_act which has been passedthrough a filter for adjusting frequency characteristics may be used.Adding the processes as described above can make the control system'sresponse characteristics to the handlebar torque further suit the tasteof the rider of the two-wheeled vehicle 1A.

Here, the gains K1 to K4 (feedback gains related to the respectivefeedback manipulated variables in the right side of the aforesaidexpression (3)) and the gain Kh, which are used for calculatingδf_dot2_cmd by the computation of the expression (3), are determined inthe aforesaid control gain determining section 35. The processing in thecontrol gain determining section 35 will now be described in detail.

The control gain determining section 35 determines the values of thegains K1 to K4 and Kh from the received estimated traveling speedVox_act and last time's desired front-wheel steering angle δf_cmd_p, bythe processing shown in the block diagram in FIG. 5.

In FIG. 5, a processing section 35-1 is a processing section whichdetermines the gain K1 in accordance with Vox_act and δf_cmd_p, and aprocessing section 35-2 is a processing section which determines thegain K2 in accordance with Vox_act and δf_cmd_p.

In the present embodiment, the processing section 35-1 determines thegain K1 from Vox_act and δf_cmd_p, in accordance with a presettwo-dimensional mapping (conversion function of two variables).Similarly, the processing section 35-2 determines the gain K2 fromVox_act and δf_cmd_p, in accordance with a preset two-dimensionalmapping (conversion function of two variables).

In these two-dimensional mappings, the trend of the change in value ofthe gain K1 with respect to Vox_act and δf_cmd_p and the trend of thechange in value of the gain K2 with respect to Vox_act and δf_cmd_p areset substantially similar to each other.

Specifically, as illustrated by the graphs shown in the processingsections 35-1 and 35-2 in FIG. 5, the two-dimensional mappings in theprocessing sections 35-1 and 35-2 are each set such that the magnitudeof the gain K1, K2 determined by the two-dimensional mapping has thetrend of monotonically decreasing with increasing Vox_act when δf_cmd_pis fixed to a given value.

Accordingly, the gains K1 and K2 as the feedback gains related to thefeedback manipulated variables having the function of stabilizing theposture in the roll direction of the vehicle body 2 of the two-wheeledvehicle 1A (making the detected roll angle φb_act and the detected rollangular velocity φb_dot_act converge respectively to φb_cmd andφb_dot_cmd) are determined such that the magnitudes of the gains K1 andK2 each become smaller as the actual traveling speed (estimatedtraveling speed Vox_act) of the two-wheeled vehicle 1A becomes greater.

In other words, the gains K1 and K2 are determined such that thesteering force that the front-wheel steering actuator 8 generates, inaccordance with a deviation of φb_act from φb_cmd or a deviation ofφb_dot_act from φb_dot_cmd, in the direction of eliminating thedeviation, is reduced when the actual traveling speed (estimatedtraveling speed Vox_act) of the two-wheeled vehicle 1A is in ahigh-speed range, as compared to when it is in a low-speed range.

Further, the two-dimensional mappings in the processing sections 35-1and 35-2 are each set such that the gain K1, K2 determined by themapping has the trend of monotonically decreasing with increasingmagnitude (absolute value) of δf_cmd_p when Vox_act is fixed to a givenvalue.

Accordingly, the gains K1 and K2 as the gains related to the feedbackmanipulated variables having the function of stabilizing the posture inthe roll direction of the vehicle body 2 of the two-wheeled vehicle 1Aare determined such that the magnitudes of the gains K1 and K2 eachbecome smaller as the magnitude of δf_cmd_p, corresponding to the actualsteering angle of the front wheel 3 f, becomes larger.

In other words, the gains K1 and K2 are determined such that thesteering force that the front-wheel steering actuator 8 generates, inaccordance with a deviation of φb_act from φb_cmd or a deviation ofφb_dot_act from φb_dot_cmd, in the direction of eliminating thedeviation, is reduced when the magnitude of the actual steering angle ofthe front wheel 3 f is large, as compared to when it is small.

Here, in the case where the magnitude of the actual steering angle ofthe front wheel 3 f is large, compared to the case where it is small,the radius of curvature of the ground contact part of the steered wheel(front wheel 3 f) as seen in a cross section including the groundcontact point of the steered wheel (front wheel 3 f) and having a normalin the X-axis direction (longitudinal direction of the vehicle body 2)becomes larger. Consequently, in the case where the magnitude of theactual steering angle of the front wheel 3 f is large, compared to thecase where it is small, the change in movement amount of the groundcontact point of the front wheel 3 f according to the change in thesteering angle becomes larger.

Because of this, if the magnitudes of the gains K1 and K2 are setindependently of the actual steering angle, oscillation is likely tooccur in the control of the posture in the roll direction of the vehiclebody 2 of the two-wheeled vehicle 1A when the actual steering angle islarge.

In view of the foregoing, in the present embodiment, it has beenconfigured such that the magnitudes of the gains K1 and K2 are changedin accordance with the magnitude of δf_cmd_p, as described above. Thiscan prevent the above-described oscillation even in the case where themagnitude (absolute value) of the actual steering angle of the frontwheel 3 f is large.

In the block diagram in FIG. 5, a processing section 35-3 is aprocessing section which determines the gain K3 in accordance withVox_act, and a processing section 35-4 is a processing section whichdetermines the gain K4 in accordance with Vox_act.

In the present embodiment, the processing sections 35-3 and 35-4determine the gains K3 and K4, respectively, from Vox_act, in accordancewith conversion functions defined by preset mappings (or arithmeticexpressions).

These conversion functions are set, as illustrated by the graphs shownin the processing sections 35-3 and 35-4 in FIG. 5, such that basicallythe gains K3 and K4 each increase monotonically, between a prescribedupper limit and a prescribed lower limit, as Vox_act increases.

In this case, in the conversion functions in the processing sections35-3 and 35-4, in the region where Vox_act takes a value near “0”, K3and K4 are each maintained at the lower limit. In the region whereVox_act takes a sufficiently large value, K3 and K4 are each maintainedat the upper limit.

As the gains K3 and K4 are determined in the above-described manner, thegains K3 and K4 as the feedback gains related to the feedbackmanipulated variables having the function of making the steering angleδf of the front wheel 3 f approach zero are determined such that themagnitudes of the gains K3 and K4 become relatively large in the casewhere the actual traveling speed (estimated traveling speed Vox_act) ofthe two-wheeled vehicle 1A is relatively high (in a high-speed range),compared to the case where the actual traveling speed of the two-wheeledvehicle 1A is relatively low (in a low-speed range (including “0”)).

In the present embodiment, as the gains K1 and K3 are set as describedabove, the ratio between the gain K1, with a fixed steering angle of thefront wheel 3 f, and the gain K3 (=K1/K3) is set such that the ratiobecomes smaller as the traveling speed of the two-wheeled vehicle 1Abecomes greater.

Similarly, as the gains K2 and K4 are set as described above, the ratiobetween the gain K2, with a fixed steering angle of the front wheel 3 f,and the gain K4 (=K2/K4) is set such that the ratio becomes smaller asthe traveling speed of the two-wheeled vehicle 1A becomes greater.

Therefore, as the traveling speed of the two-wheeled vehicle 1A becomesgreater, the gains K1 and K2 as the feedback gains related to thefeedback manipulated variables having the function of controlling theposture in the roll direction of the vehicle body 2 each becomerelatively small compared to the gains K3 and K4 as the feedback gainsrelated to the feedback manipulated variables having the function ofmaking the actual steering angle of the front wheel 3 f converge tozero.

Accordingly, in the case where the actual traveling speed (estimatedtraveling speed Vox_act) of the two-wheeled vehicle 1A is relativelyhigh, i.e. in the state where the stability of the posture in the rolldirection of the vehicle body 2 is high, a rider of the two-wheeledvehicle 1A can readily change the posture in the roll direction (rollangle φb) of the vehicle body 2 by shifting the weight of the rider'sbody and so on, as in the case of a conventional two-wheeled vehicle(which is not provided with the function of controlling the posture inthe roll direction of the vehicle body).

It should be noted that the two-dimensional mappings for determining thegains K1 and K2 may each be set such that the value of K1, K2 isdetermined to be “0” or almost “0” when the estimated traveling speedVox_act reaches a certain level (i.e. when Vox_act is not lower than aprescribed speed).

With this configuration, the function of controlling the posture in theroll direction of the vehicle body 2 becomes substantially OFF when theactual traveling speed (estimated traveling speed Vox_act) of thetwo-wheeled vehicle 1A is relatively high. This can make the behavioralcharacteristics of the two-wheeled vehicle 1A approach thecharacteristics comparable to those of a conventional two-wheeledvehicle in the case where the actual traveling speed of the two-wheeledvehicle 1A is high.

Further, in FIG. 5, a processing section 35-5 represents a processingsection which determines the gain Kh in accordance with Vox_act.

In the present embodiment, the processing section 35-5 determines thegain Kh from Vox_act, in accordance with a conversion function definedby a preset mapping (or arithmetic expression), as with the gains K3 andK4.

This conversion function is set, as illustrated by the graph shown inthe processing section 35-5 in FIG. 5, such that basically the magnitudeof the gain Kh becomes relatively large when Vox_act is large ascompared to when Vox_act is small.

In this case, the conversion function in the processing section 35-5 isset such that the gain Kh increases monotonically, between a prescribedupper limit and a prescribed lower limit, as Vox_act increases. Further,the conversion function is set such that the Kh determined thereby hassaturation characteristics with respect to Vox_act. That is, Kh isdetermined by the conversion function such that the magnitude of therate of change of the value of Kh with respect to Vox_act (increase ofKh per unit increase of Vox_act) becomes smaller in a low-speed range inwhich Vox_act takes a value near “0” (including “0”) and a high-speedrange in which Vox_act takes a sufficiently large value, than in amid-speed range between the low-speed range and the high-speed range.

Determining the gain Kh in accordance with Vox_act in this mannerensures that the magnitude of the gain Kh relative to the gain K1becomes large when the actual traveling speed of the two-wheeled vehicle1A is relatively high.

Accordingly, when a rider applies a torque about the handlebar axis Chto the operation apparatus 7 in an attempt to move the operationapparatus 7, the desired front-wheel steering angular accelerationδf_dot2_cmd is determined so as to bring the detected handlebar torqueTh_act to zero. This leads to improved tracking of the steering of thefront wheel 3 f to the rider's moving the operation apparatus 7.

As a result, during high-speed traveling of the two-wheeled vehicle 1A,the rider can steer the front wheel 3 f by manipulating the operationapparatus 7, similarly as in a conventional two-wheeled vehicle.

The above has described the details of the processing in the controlgain determining section 35 according to the present embodiment.

It should be noted that the gain K3 may be set such that, instead ofincreasing monotonically, it remains constant or decreasesmonotonically, between a prescribed upper limit and a prescribed lowerlimit, as Vox_act increases. In this case as well, the ratio between thegain K1, with a fixed steering angle of the front wheel 3 f, and thegain K3 (=K1/K3) is set such that the ratio becomes smaller as thetraveling speed of the two-wheeled vehicle 1A becomes greater.

Similarly, the gain K4 may be set such that, instead of increasingmonotonically, it remains constant or decreases monotonically, between aprescribed upper limit and a prescribed lower limit, as Vox_actincreases. In this case as well, the ratio between the gain K2, with afixed steering angle of the front wheel 3 f, and the gain K4 (=K2/K4) isset such that the ratio becomes smaller as the traveling speed of thetwo-wheeled vehicle 1A becomes greater.

Further, the gains K3 and K4 may be determined in accordance withVox_act and δf_cmd_p, as with the gains K1 and K2. For example, when apole placement method or the like is used to obtain rough approximationsof appropriate values for the set of gains K1 to K4 such that the ratiobetween the gain K1, with a fixed steering angle of the front wheel 3 f,and the gain K3 (=K1/K3) becomes smaller as the traveling speed of thetwo-wheeled vehicle 1A becomes greater, the gains K3 and K4 also takevalues dependent on δf_cmd_p. Therefore, the gains K3 and K4 are alsopreferably determined in accordance with Vox_act and δf_cmd_p, as withthe gains K1 and K2, so that the values approach the approximations ofthe appropriate values obtained from the pole placement method or thelike.

Further, for the conversion functions for determining the gains K1 andK2, conversion functions in other forms may be adopted, as long as theycan determine the gains with the above-described trends with respect toVox_act and δf_cmd_p. The conversion functions may each be set in a formother than the two-dimensional mapping (for example, one-dimensionalmapping and arithmetic expression may be combined). The same applies tothe case where the gains K3 and K4 are each determined by a conversionfunction in accordance with Vox_act and δf_cmd_p, or by a conversionfunction in accordance with Vox_act. Furthermore, for the conversionfunction for determining the gain Kh, a conversion function in anotherform may be adopted, as long as it can determine the gain with theabove-described trend with respect to Vox_act.

The last time's desired front-wheel steering angle δf_cmd_p has themeaning as a pseudo estimate (alternative observed value) of the actualsteering angle of the front wheel 3 f at the current time.

Accordingly, for determining the respective gains K1, K2, K3, K4, andKh, the aforesaid detected front-wheel steering angle δf_act may be usedinstead of δf_cmd_p.

Further, in the case where the response of the front-wheel drivingactuator 10 is sufficiently quick, the value of the traveling speed(=Vf_cmd_p*cos(δf_cmd_p*cos(θcf)), hereinafter referred to as “lasttime's desired traveling speed Vox_cmd_p”) calculated by the computationsimilar to that in the aforesaid expression (2) from the above-describedlast time's desired front-wheel steering angle δf_cmd_p and a lasttime's desired front-wheel rotational transfer velocity Vf_cmd_p(desired front-wheel rotational transfer velocity Vf_cmd determined bythe desired front-wheel rotational transfer velocity determining section36 in the last time's control processing cycle) has the meaning as apseudo estimate (alternative observed value) of the actual travelingspeed of the two-wheeled vehicle 1A at the current time.

Accordingly, for determining the respective gains K1, K2, K3, K4, andKh, the above-described last time's desired traveling speed Vox_cmd_pmay be used instead of Vox_act.

After the control device 15 has determined the desired front-wheelsteering angle δf_cmd in the posture control arithmetic section 37 asdescribed above, the control device 15 carries out the processing in thedesired handlebar angle determining section 38.

The desired handlebar angle determining section 38 receives, as shown inFIG. 3, the estimated traveling speed Vox_act calculated in theestimated traveling speed calculating section 33 and the desiredfront-wheel steering angle δf_cmd determined in the posture controlarithmetic section 37.

The desired handlebar angle determining section 38 uses these inputvalues to carry out the processing shown in the block diagram in FIG. 9,to thereby determine a desired handlebar angle δh_cmd and a desiredhandlebar angular velocity δh_dot_cmd.

In FIG. 9, a processing section 38-1 is a processing section whichdetermines a correction factor Kh_v for correcting δf_cmd, in accordancewith the estimated traveling speed Vox_act, a processing section 38-2 isa processing section which corrects δf_cmd by multiplying δf_cmd by theoutput (correction factor Kh_v) from the processing section 38-1, aprocessing section 38-3 is a processing section which determines adesired handlebar angle δh_cmd from the output (=Kh_v*δf_cmd) from theprocessing section 38-2, and a processing section 38-4 is a processingsection which calculates a temporal change rate (amount of change perunit time) of the output (δh_cmd) from the processing section 38-3, as adesired handlebar angular velocity δh_dot_cmd.

Accordingly, the desired handlebar angle determining section 38determines a desired handlebar angle δh_cmd in accordance with thecorrected value (=Kh_v*δf_cmd, this corrected value will be hereinafterreferred to as “corrected desired front-wheel steering angle δf_cmd_c”)obtained by correcting δf_cmd in accordance with Vox_act. Further, thedesired handlebar angle determining section 38 differentiates thisδh_cmd to determine a desired handlebar angular velocity δh_dot_cmd.

In this case, the correction factor Kh_v takes a positive value of 1 orless. The correction factor Kh_v is determined from the estimatedtraveling speed Vox_act, by a preset conversion function. The conversionfunction is defined, for example, by a mapping or an arithmeticexpression. The conversion function is set to show the trend asillustrated by the graph shown in the processing section 38-1 in FIG. 9.

Here, when the two-wheeled vehicle 1A is stationary or traveling at avery low speed, the posture restoring force in the roll direction of thevehicle body 2 per unit steering angle of the front wheel 3 f is weakand, therefore, the front wheel 3 f needs to be steered relativelylargely for stabilizing the posture.

In such a case, if it is set such that the steering angle δf of thefront wheel 3 f coincides with the handlebar angle δh as in aconventional two-wheeled vehicle in which the operation apparatus isdirectly connected to the steering shaft of the front wheel, the largesteering of the front wheel 3 f will cause the operation apparatus 7 torotate largely, giving a sense of discomfort to the rider of thetwo-wheeled vehicle 1A. The operation apparatus 7 may also interferewith a part of the vehicle body 2 close to the operation apparatus 7.

In order to solve the above problems, in the present embodiment, theconversion function in the processing section 38-1 has been set, asillustrated by the graph in the figure, such that the correction factorKh_v becomes smaller as Vox_act becomes smaller (as the actual travelingspeed of the two-wheeled vehicle 1A becomes lower).

This correction factor Kh_v basically has the function of changing theratio of the amount of change of the handlebar angle δh to the unitamount of change of the steering angle δf of the front wheel 3 f, i.e. aso-called steering gear ratio, in accordance with Vox_act. Therefore, itis set such that the above-described ratio becomes smaller as Vox_actbecomes smaller.

More specifically, the conversion function in the processing section38-1 is set such that the above-described ratio (correction factor Kh_v)becomes “1” or almost “1” when Vox_act becomes a prescribed speed orhigher and that the ratio becomes less than “1” when Vox_act becomeslower than the prescribed speed.

As a result, when the two-wheeled vehicle 1A is stationary or travelingat a very low speed, even if the steering angle of the front wheel 3 fbecomes large for the purpose of stabilizing the posture of the vehiclebody 2, the handlebar angle δh is restricted to a small angle. This canreduce the sense of discomfort of the rider of the two-wheeled vehicle1A and also prevent the interference between the operation apparatus 7and the vehicle body 2.

Furthermore, in the present embodiment, when the processing section 38-3determines a desired handlebar angle δh_cmd from the corrected desiredfront-wheel steering angle δf_cmd_c which is δf_cmd corrected with thecorrection factor Kh_v, it determines δh_cmd in accordance with aconversion function which has been preset to cause δh_cmd to havesaturation characteristics with respect to δf_cmd_c. The saturationcharacteristics means the characteristics that the magnitude of the rateof change of δh_cmd with respect to δf_cmd_c (amount of change of δh_cmdper unit amount of change of δf_cmd_c) becomes smaller when themagnitude of δh_cmd_c is large, as compared to when the magnitude ofδh_cmd_c is small.

The conversion function in the processing section 38-3 having suchsaturation characteristics is defined, for example, by a mapping or anarithmetic expression. The conversion function is set, for example, asillustrated by the graph shown in the processing section 38-3 in FIG. 9.

In this example, δh_cmd is determined such that, when the magnitude(absolute value) of δf_cmd_c is not greater than a prescribed value,δh_cmd changes monotonically up to an upper limit on the positive sideor down to a lower limit on the negative side in response to the changeof δf_cmd_c (or δf_cmd) to the positive side or the negative side,respectively. In this situation, δh_cmd is determined, for example, tocoincide with, or almost coincide with, δf_cmd_c.

When the magnitude (absolute value) of δf_cmd_c exceeds the prescribedvalue, δh_cmd is maintained constantly at the upper limit on thepositive side or the lower limit on the negative side.

Determining δh_cmd so as to have saturation characteristics with respectto δf_cmd_c in the above-described manner can prevent the actualhandlebar angle (detected handlebar angle δh_act) from becomingexcessively large.

It should be noted that the processing of determining δh_cmd fromδf_cmd_c may be carried out by using, for example, a conversion function(having saturation characteristics) as illustrated by the graph shown ina processing section 38-5 in the block diagram in FIG. 10. Thisconversion function, defined by a mapping or an arithmetic expression,is set such that the magnitude of the rate of change of δh_cmd withrespect to δf_cmd_c becomes continuously smaller as the magnitude ofδf_cmd_c becomes larger. The minimum value of the magnitude of theabove-described rate of change may be greater than zero.

When the conversion function in the processing section 38-5 is set inthe above-described manner, the rate of change of δh_cmd with respect toδf_cmd (amount of change of δh_cmd per unit increase of δf_cmd) can bemade to change continuously. Consequently, the angular acceleration ofthe actual handlebar angle can be made to change continuously. This canrestrict an abrupt change in rotational angular velocity (angularvelocity about the handlebar axis Ch) of the operation apparatus 7, andaccordingly, the sense of discomfort of the rider during themanipulation of the operation apparatus 7 can further be reduced. Theload of the handlebar driving actuator 9 can be reduced as well.

It should be noted that δh_cmd may be determined from δf_cmd and Vox_actby a two-dimensional mapping. Further, as Vox_act for determiningδh_cmd, the value of the actual rotational transfer velocity of the rearwheel 3 r, obtained by multiplying an observed value of the actualrotational angular velocity of the rear wheel 3 r (value detected by anappropriate detector such as a rotary encoder) by the effective rollingradius of the rear wheel 3 r, may be used. Alternatively, the aforesaidlast time's desired traveling speed Vox_cmd_p, calculated by thecomputation similar to that in the right side of the aforesaidexpression (2) from the last time's desired front-wheel steering angleδf_cmd_p and the last time's desired front-wheel rotational transfervelocity Vf_cmd_p, may be used instead of Vox_act.

Controls of the aforesaid front-wheel steering actuator 8, handlebardriving actuator 9, and front-wheel driving actuator 10 will now bedescribed.

The control device 15 further includes, as functions other than thefunctions shown in FIG. 3, a front-wheel steering actuator controlsection 41 shown in FIG. 11, a front-wheel driving actuator controlsection 42 shown in FIG. 12, and a handlebar driving actuator controlsection 43 shown in FIG. 13.

The front-wheel steering actuator control section 41 carries out drivecontrol of the front-wheel steering actuator 8, by the controlprocessing shown in the block diagram in FIG. 11, for example, to causethe actual steering angle (detected front-wheel steering angle δf_act)of the front wheel 3 f to track a desired front-wheel steering angleδf_cmd.

In this example, the front-wheel steering actuator control section 41receives a desired front-wheel steering angle δf_cmd, a desiredfront-wheel steering angular velocity δf_dot_cmd, and a desiredfront-wheel steering angular acceleration δf_dot2_cmd determined in theabove-described manner in the posture control arithmetic section 37, adetected front-wheel steering angle δf_act, and a detected front-wheelsteering angular velocity δf_dot_act which is a detected value of theactual steering angular velocity of the front wheel 3 f.

It should be noted that the detected front-wheel steering angularvelocity δf_dot_act is a value of the steering angular velocity which isrecognized on the basis of an output from the front-wheel steering angledetector 17, or a value obtained by calculating a temporal change rateof the detected front-wheel steering angle δf_act.

The front-wheel steering actuator control section 41 determines, fromthe above-described input values, an electric current command valueI_δf_cmd which is a desired value of the electric current passed throughthe front-wheel steering actuator 8 (electric motor), by the processingin an electric current command value determining section 41-1.

The electric current command value determining section 41-1 determinesthe electric current command value I_δf_cmd by summing up a feedbackmanipulated variable component obtained by multiplying a deviation ofδf_act from δf_cmd by a gain Kδf_p of a prescribed value, a feedbackmanipulated variable component obtained by multiplying a deviation ofδf_dot_act from δf_dot_cmd by a gain Kδf_v of a prescribed value, and afeedforward manipulated variable component obtained by multiplyingδf_dot2_cmd by a gain Kδf_a of a prescribed value, as shown by thefollowing expression (5).

$\begin{matrix}{{{I\_\delta f}{\_ cmd}} = {{{K\delta f\_ p}*\left( {{\delta f\_ cmd} - {\delta f\_ act}} \right)} + {{K\delta f\_ v}*\left( {{{\delta f\_ dot}{\_ cmd}} - {{\delta f\_ dot}{\_ act}}} \right)} + {{K\delta f\_ a}*{\delta f\_ dot2}{\_ cmd}}}} & (5)\end{matrix}$

The front-wheel steering actuator control section 41 then controls theactual electric current passed through the front-wheel steering actuator8 (electric motor) to match the electric current command value I_δf_cmd,by an electric current control section 41-2 which is made up of a motordriver or the like.

In this manner, the control is performed such that the actual steeringangle of the front wheel 3 f tracks the desired front-wheel steeringangle δf_cmd. In this case, the electric current command value I_δf_cmdincludes the third term in the right side of the above expression (5),i.e. the feedforward manipulated variable component, ensuring improvedtracking in the above-described control.

It should be noted that the technique of controlling the front-wheelsteering actuator 8 to cause the actual steering angle of the frontwheel 3 f to track the desired front-wheel steering angle δf_cmd is notlimited to the above-described technique; other techniques may be usedas well. For example, various kinds of known servo control techniquesrelated to electric motors (feedback control techniques for causing theactual angle of rotation of the rotor of the electric motor to track adesired value) may be adopted.

The front-wheel driving actuator control section 42 carries out drivecontrol of the front-wheel driving actuator 10, by the controlprocessing shown in the block diagram in FIG. 12, for example, to causethe actual rotational transfer velocity of the front wheel 3 f to tracka desired front-wheel rotational transfer velocity Vf_cmd (or to causethe actual rotational angular velocity of the front wheel 3 f to track adesired rotational angular velocity corresponding to Vf_cmd).

In this example, the front-wheel driving actuator control section 42receives a desired front-wheel rotational transfer velocity Vf_cmddetermined in the above-described manner in the desired front-wheelrotational transfer velocity determining section 36, and an estimatedfront-wheel rotational transfer velocity Vf_act.

The front-wheel driving actuator control section 42 determines, from theabove-described input values, an electric current command value I_Vf_cmdwhich is a desired value of the electric current passed through thefront-wheel driving actuator 10 (electric motor), by the processing inan electric current command value determining section 42-1.

The electric current command value determining section 42-1 determines afeedback manipulated variable component obtained by multiplying adeviation of Vf_act from Vf_cmd by a gain KVf_v of a prescribed value,as the electric current command value I_Vf_cmd, as shown by thefollowing expression (6).

I _(—) Vf_cmd=KVf _(—) v*(Vf_cmd−Vf_act)  (6)

It should be noted that, instead of using the above expression (6),I_Vf_cmd may be determined by, for example, multiplying a deviation ofthe detected value of the actual rotational angular velocity of thefront wheel 3 f, which is indicated by an output from the front-wheelrotational speed detector 20, from a value obtained by dividing Vf_cmdby the effective rolling radius of the front wheel 3 f (i.e. a desiredvalue of the rotational angular velocity of the front wheel 3 f) by again of a prescribed value.

The front-wheel driving actuator control section 42 then controls theactual electric current passed through the front-wheel driving actuator10 (electric motor) to match the electric current command valueI_Vf_cmd, by an electric current control section 42-2 which is made upof a motor driver or the like.

In this manner, the control is performed such that the actual rotationaltransfer velocity of the front wheel 3 f tracks the desired front-wheelrotational transfer velocity Vf_cmd (or such that the actual rotationalangular velocity tracks the desired value of the rotational angularvelocity corresponding to Vf_cmd).

It should be noted that the technique of controlling the front-wheeldriving actuator 10 to cause the actual rotational transfer velocity ofthe front wheel 3 f to track the desired front-wheel rotational transfervelocity Vf_cmd is not limited to the above-described technique; othertechniques may be used as well. For example, various kinds of knownspeed control techniques related to electric motors (feedback controltechniques for causing the actual rotational angular velocity of therotor of the electric motor to track a desired value) may be adopted.

The handlebar driving actuator control section 43 carries out drivecontrol of the handlebar driving actuator 9, by the control processingshown in the block diagram in FIG. 13, for example, to cause the actualrotational angle (handlebar angle) of the operation apparatus 7 to tracka desired handlebar angle δh_cmd.

In this example, the handlebar driving actuator control section 43receives a desired handlebar angle δh_cmd and a desired handlebarangular velocity δh_dot_cmd determined in the above-described manner inthe desired handlebar angle determining section 38, a detected handlebarangle δh_act which is a detected value of the actual rotational angle ofthe operation apparatus 7, and a detected handlebar angular velocityδh_dot_act which is a detected value of the actual rotational angularvelocity of the operation apparatus 7.

It should be noted that the detected handlebar angle δh_act and thedetected handlebar angular velocity δh_dot_act are a value of thehandlebar angle which is recognized on the basis of an output from thehandlebar angle detector 18 and a value indicating a temporal changerate thereof, respectively.

The handlebar driving actuator control section 43 determines, from theabove-described input values, an electric current command value I_δh_cmdwhich is a desired value of the electric current passed through thehandlebar driving actuator 9 (electric motor), by the processing in anelectric current command value determining section 43-1.

The electric current command value determining section 43-1 determinesthe electric current command value I_δh_cmd by summing up a feedbackmanipulated variable component obtained by multiplying a deviation ofδh_act from δh_cmd by a gain Kδh_p of a prescribed value and a feedbackmanipulated variable component obtained by multiplying a deviation ofδh_dot_act from δh_dot_cmd by a gain Kδh_v of a prescribed value, asshown by the following expression (7).

$\begin{matrix}{{{I\_\delta h}{\_ cmd}} = {{{K\delta h\_ p}*\left( {{\delta h\_ cmd} - {\delta h\_ act}} \right)} + {{K\delta h\_ v}*\left( {{{\delta h\_ dot}{\_ cmd}} - {{\delta h\_ dot}{\_ act}}} \right)}}} & (7)\end{matrix}$

The handlebar driving actuator control section 43 then controls theactual electric current passed through the handlebar driving actuator 9(electric motor) to match the electric current command value I_δh_cmd,by an electric current control section 43-2 which is made up of a motordriver or the like.

In this manner, the control is performed such that the actual handlebarangle of the operation apparatus 7 tracks the desired handlebar angleδh_cmd.

It should be noted that the technique of controlling the handlebardriving actuator 9 to cause the actual handlebar angle of the operationapparatus 7 to track the desired handlebar angle δh_cmd is not limitedto the above-described technique; various kinds of known servo controltechniques, for example, may be adopted.

The above has described the details of the control processing in thecontrol device 15 according the present embodiment.

Here, the correspondence between the present embodiment and the presentinvention will be described. In the present embodiment, the front wheel3 f corresponds to the steered wheel in the present invention, thefront-wheel steering actuator 8 (electric motor) corresponds to thesteering actuator in the present invention, and the handlebar drivingactuator 9 corresponds to the handlebar actuator in the presentinvention.

Further, in the example of the present embodiment, the first motionalstate quantity in the present invention (motional state quantity of theinclination angle in the roll direction (roll angle) of the vehicle body2) is made up of a value of the roll angle φb as it is and a rollangular velocity φb_dot which is a temporal change rate of the rollangle.

Further, in the example of the present embodiment, the second motionalstate quantity in the present invention (motional state quantity of thesteering angle of the steered wheel (front wheel 3 f)) is made up of avalue of the steering angle δf, as it is, of the front wheel 3 f and asteering angular velocity δf_dot which is a temporal change rate of thesteering angle.

In the present embodiment, the desired values (φb_cmd, φb_dot_cmd) ofthe roll angle φb and the roll angular velocity φb_dot constituting thefirst motional state quantity are each set to zero, and the desiredvalues of the steering angle δf and the steering angular velocity δf_dotconstituting the second motional state quantity are each set to zero.

In the processing in the posture control arithmetic section 37, adesired front-wheel steering angular acceleration δf_dot2_cmd as anoperational target of the front-wheel steering actuator 8 (steeringactuator) is determined, by a feedback control law, so as to cause adeviation of each of the detected roll angle φb_act, the detected rollangular velocity φb_dot_act, the last time's desired front-wheelsteering angle δf_cmd_p, representing a pseudo estimate of the steeringangle δf, and the last time's desired front-wheel steering angularvelocity δf_dot_cmd_p, representing a pseudo estimate of the steeringangular velocity δf_dot, from the corresponding desired value toconverge to zero.

Further, the steering force of the front-wheel steering actuator 8 iscontrolled by the aforesaid front-wheel steering actuator controlsection 41 such that the actual steering angle of the front wheel 3 ftracks a desired front-wheel steering angle δf_cmd which has beendetermined by performing integration twice on the above-describedδf_dot2_cmd.

In this manner, the front-wheel steering actuator 8 is controlled so asto stabilize the first motional state quantity (motional state quantityof the inclination angle in the roll direction of the vehicle body 2)and the second motional state quantity (motional state quantity of thesteering angle of the steered wheel (front wheel 3 f)) and, hence, tostabilize the posture (in the roll direction) of the vehicle body 2.

It should be noted that in the present embodiment, the desiredfront-wheel steering angular acceleration δf_dot2_cmd of the steeredwheel (front wheel 3 f) corresponds to the reference quantity in thepresent invention.

Further, in the present embodiment, the aforesaid gain K1 corresponds tothe sensitivity Ra1 of the change in value of the reference quantity(δf_dot2_cmd) to the change in observed value (φb_act) of theinclination angle in the roll direction of the vehicle body 2, and theaforesaid gain K2 corresponds to the sensitivity Ra2 of the change invalue of the reference quantity (δf_dot2_cmd) to the change in observedvalue (φb_dot_act) of the temporal change rate of the inclination anglein the roll direction of the vehicle body 2.

Furthermore, the aforesaid gain K3 corresponds to the sensitivity Rb1 ofthe change in value of the reference quantity (δf_dot2_cmd) to thechange in observed value (δf_act) of the steering angle δf of thesteered wheel (front wheel 3 f), and the aforesaid gain K4 correspondsto the sensitivity Rb2 of the change in value of the reference quantity(δf_dot2_cmd) to the change in observed value (δf_dot_act) of thetemporal change rate of the steering angle δf of the steered wheel(front wheel 3 f).

In this case, as the gains K1, K2, K3, and K4 are determined with theabove-described trends with respect to the observed value (Vox_act) ofthe actual traveling speed of the two-wheeled vehicle 1A, the steeringforce of the front-wheel steering actuator 8 is controlled such that themagnitude of the ratio K1/K3 between the gains K1 and K3, correspondingto the ratio Ra1/Rb1 between the above-described sensitivities Ra1 andRb1, becomes smaller as the magnitude of the observed value (Vox_act) ofthe traveling speed of the two-wheeled vehicle 1A becomes larger.Further, the steering force of the front-wheel steering actuator 8 iscontrolled such that the magnitude of the ratio K2/K4 between the gainsK2 and K4, corresponding to the ratio Ra2/Rb2 between theabove-described sensitivities Ra2 and Rb2, becomes smaller as themagnitude of the observed value (Vox_act) of the traveling speed of thetwo-wheeled vehicle 1A becomes larger.

Further, as the gains K1 and K2 are determined with the above-describedtrends with respect to the observed value (δf_act) of the steering angleof the steered wheel (front wheel 3 f), the steering force of thefront-wheel steering actuator 8 is controlled such that the magnitudesof the gains K1 and K2 corresponding respectively to the above-describedsensitivities Ra1 and Ra2 each become smaller as the magnitude of theobserved value (δf_act) of the steering angle of the steered wheel(front wheel 3 f) from the non-steered state thereof becomes larger.

Further, as the desired handlebar angle δh_cmd is determined by theprocessing shown in FIG. 9 or 10 (particularly, the processing in theprocessing section 38-3 or 38-5), the handlebar driving actuator 9 iscontrolled such that the handlebar angle δh representing the rotationalamount of the operation apparatus 7 has saturation characteristics withrespect to the steering angle δf of the steered wheel (front wheel 3 f)from the non-steered state thereof.

According to the present embodiment described above, when thetwo-wheeled vehicle 1A is stopped or traveling at a low speed, in thecase where the actual roll angle (detected roll angle φb_act) of thevehicle body 2 deviates from the desired roll angle φb_cmd (in otherwords, in the case where the actual posture of the vehicle body 2deviates from a desired posture satisfying φb_act=φb_cmd), the steeringof the front wheel 3 f by the steering force of the front-wheel steeringactuator 8 can cause a moment (in the roll direction) capable of makingthe actual roll angle of the vehicle body 2 restored to the desired rollangle φb_cmd to act on the vehicle body 2, without the need for therider to intentionally move the operation apparatus 7.

That is, it is possible to cause the moment in the roll direction forstabilizing the posture of the vehicle body 2 to act on the vehicle body2. With this moment, the actual roll angle of the vehicle body 2 isrestored to the desired roll angle φb_cmd.

Further, through calculation of the desired front-wheel steering angularacceleration δf_dot2_cmd by the aforesaid expression (3) (or expression(4)), the desired front-wheel steering angular acceleration δf_dot2_cmd(operational target of the front-wheel steering actuator 8) isdetermined such that a deviation (φb_cmd−φb_act) of the detected rollangle φb_act, representing an observed value of the current actual rollangle, from the desired roll angle φb_cmd of the vehicle body 2, adeviation (φb_dot_cmd−φb_dot_act) of the detected roll angular velocityφb_dot_act, representing an observed value of the current actual rollangular velocity, from the desired roll angular velocity φb_dot_cmd ofthe vehicle body 2, the last time's desired front-wheel steering angleδf_cmd_p, representing a pseudo estimate of the current actual steeringangle (from the neutral steering angle) of the front wheel 3 f, and thelast time's desired front-wheel steering angular velocity δf_dot_cmd_p,representing a pseudo estimate of the angular velocity of the currentactual steering angle of the front wheel 3 f, each approach “0” in thestate where the rider is not attempting to move the operation apparatus7.

Therefore, the steering angle of the front wheel 3 f is controlled so asto cause the actual roll angle and roll angular velocity of the vehiclebody 2 to converge to the respective desired values (zero in the presentembodiment), while preventing the actual steering angle of the frontwheel 3 f from diverging from the neutral steering angle (while causingthe actual steering angle to ultimately converge to the neutral steeringangle).

Accordingly, the posture of the vehicle body 2 can be stabilizedsmoothly, particularly when the two-wheeled vehicle 1A is stopped ortraveling at a low speed. Further, the two-wheeled vehicle 1A can bestarted smoothly with the vehicle body 2 in a stable posture.

In the case where a rider applies a rotative force (about the handlebaraxis Ch) to the operation apparatus 7 in an attempt to move theoperation apparatus 7, the steering angle of the front wheel 3 f can becontrolled with an angular acceleration corresponding to the magnitudeof the rotative force applied to the operation apparatus 7, by thefeedforward manipulated variable Th_act*Kh.

Further, the gains K1 and K2, which are the feedback gains related tothe posture control in the roll direction of the vehicle body 2, and thegains K3 and K4, which are the feedback gains related to the control ofthe steering angle of the front wheel 3 f, are variably determined, asdescribed above, in accordance with the estimated traveling speedVox_act, which is an observed value of the current actual travelingspeed (transfer velocity in the X-axis direction) of the two-wheeledvehicle 1A.

Accordingly, when the two-wheeled vehicle 1A is stopped or traveling ata low speed, it is possible to perform the steering of the front wheel 3f to cause the actual roll angle of the vehicle body 2 to quicklyapproach the desired roll angle φb_cmd.

In the state where the two-wheeled vehicle 1A is traveling at a highspeed, even if the vehicle body 2 is leaned, the steering control of thefront wheel 3 f for causing the actual roll angle of the vehicle body 2to approach the desired roll angle φb_cmd is not performed, or suchsteering control is restricted. Consequently, a rider can readily turnthe two-wheeled vehicle 1A by banking the vehicle body 2 by shifting theweight of the rider's body, as with a conventional two-wheeled vehicle.

Furthermore, the gains K1 and K2 are not only determined variably inaccordance with the estimated traveling speed Vox_act, but alsodetermined variably in accordance with the last time's desiredfront-wheel steering angle δf_cmd_p, representing a pseudo estimate ofthe current actual steering angle of the front wheel 3 f, as describedabove. Accordingly, good posture control of the vehicle body 2 can beachieved with high robustness over a wide steering range of the frontwheel 3 f, without causing oscillation in the posture control of thevehicle body 2.

Second Embodiment

A second embodiment of the present invention will be described belowwith reference to FIGS. 14 to 22.

Referring to FIG. 14, a mobile vehicle 201A according to the presentembodiment is a two-wheeled vehicle which includes a vehicle body 202,and a front wheel 203 f and a rear wheel 203 r arranged spaced apartfrom each other in the longitudinal direction of the vehicle body 202.Hereinafter, the mobile vehicle 201A will be referred to as “two-wheeledvehicle 201A”.

On the upper surface of the vehicle body 202, a seat 206 is provided fora rider to sit astride.

At the front portion of the vehicle body 202, a front-wheel supportmechanism 204 for axially supporting the front wheel 203 f, and anoperation apparatus 207 for a rider who has sat on the seat 206 to holdare mounted.

The front-wheel support mechanism 204 is made up of a front fork whichincludes a suspension mechanism such as a damper, for example. Themechanical structure of the front-wheel support mechanism is similar tothat of a conventional motorcycle, for example. At one end of thisfront-wheel support mechanism 204 (at its end on the front side of thevehicle body 202), the front wheel 203 f is axially supported, viabearings or the like, such that it can rotate about the axle centerline(rotational axis of the front wheel 203 f) that extends in the directionorthogonal to the diameter direction of the front wheel 203 f (in thedirection perpendicular to the paper plane of FIG. 14).

The front-wheel support mechanism 204 is mounted to the front portion ofthe vehicle body 202 such that the mechanism can rotate about a steeringaxis Csf which is tilted backward. This configuration makes the frontwheel 203 f serve as a steered wheel which can be rotated, or, steeredabout the steering axis Csf together with the front-wheel supportmechanism 204.

The operation apparatus 207 is mounted to the front portion of thevehicle body 202 so as to be able to rotate about the steering axis Csfof the front wheel 203 f in an integrated manner with the front-wheelsupport mechanism 204. Although not shown in detail in the figure, thisoperation apparatus 207 is equipped with an accelerator grip, brakelever, turn signal switch, and so on, as with the handlebar of aconventional motorcycle.

The rear portion of the vehicle body 202 is extended to over the rearwheel 203 r. At the rear end portion of the vehicle body 202, arear-wheel support mechanism 205 for axially supporting the rear wheel203 r in a rotatable manner and an actuator 208 for generating asteering force for steering the rear wheel 203 r are mounted.

The rear-wheel support mechanism 205 is made up of a suspensionmechanism including a damper and a swing arm. The rear-wheel supportmechanism 205 is arranged to extend downward from the rear end portionof the vehicle body 202.

At the lower end of the rear-wheel support mechanism 205, the rear wheel203 r is axially supported, via bearings or the like, such that it canrotate about the axle centerline (rotational axis of the rear wheel 203r) that extends in the direction orthogonal to the diameter direction ofthe rear wheel 203 r (in the direction perpendicular to the paper planeof FIG. 14).

In the present embodiment, an actuator 209 for rotatively driving therear wheel 203 r about its axle centerline is attached to the axle ofthe rear wheel 203 r. The actuator 209 serves as a power engine whichgenerates a thrust force for the two-wheeled vehicle 201A. In thepresent embodiment, this actuator 209 (hereinafter, also referred to as“rear-wheel driving actuator 209”) is made up of an electric motor (witha speed reducer).

It should be noted that the actuator 209 may be made up of a hydraulicactuator, for example, instead of the electric motor. Alternatively, theactuator 209 may be made up of an internal combustion engine.Furthermore, the actuator 209 may be attached to the vehicle body 202 ata position apart from the axle of the rear wheel 203 r, and the actuator209 and the axle of the rear wheel 203 r may be connected by anappropriate power transmission device.

The two-wheeled vehicle 201A may be equipped, not with the actuator 209for rotatively driving the rear wheel 203 r about its axle centerline,but with an actuator for rotatively driving the front wheel 203 f aboutits axle centerline. Alternatively, the two-wheeled vehicle 201A may beequipped with an actuator for rotatively driving the front wheel 203 fand the rear wheel 203 r about their respective axle centerlines.

The rear-wheel support mechanism 205 is mounted to the vehicle body 202such that the mechanism can rotate about a steering axis Csr which istilted backward. This configuration makes the rear wheel 203 r serve asa steered wheel which can be rotated, or, steered about the steeringaxis Csr together with the rear-wheel support mechanism 205. As thesteering axis Csr is tilted backward, the rear wheel 203 r has apositive caster angle θcr.

Supplementally, in the two-wheeled vehicle 201A of the presentembodiment, the relative arrangement of the steering axis Csr and therear wheel 203 r in the basic posture state in which the two-wheeledvehicle 201A is stationary in the straight-ahead posture is set, asshown in FIG. 14, such that an intersection point Er′ of the steeringaxis Csr and a straight line connecting the center of the axle of therear wheel 203 r and the ground contact point thereof is located belowthe ground surface 110 (or, such that a height a′ of the intersectionpoint Er′ from the ground surface 110 is lower (a′<0) than the groundsurface 110) in the basic posture state.

In other words, the relative arrangement of the steering axis Csr andthe rear wheel 203 r in the above-described basic posture state is setsuch that the point of intersection of the steering axis Csr and theground surface 110 is located behind the ground contact point of therear wheel 203 r (such that the rear wheel 203 r has a negative trail)in the basic posture state.

It should be noted that the basic posture state of the two-wheeledvehicle 201A more specifically refers to the state where the front wheel203 f and the rear wheel 203 r are both stationary in the uprightposture in contact with the ground surface 110 and the axle centerlines(centers of the rotational axes) of the front wheel 203 f and the rearwheel 203 r extend in parallel with each other in the directionorthogonal to the longitudinal direction of the vehicle body 202.

In the two-wheeled vehicle 201A according to the present embodiment, therelative arrangement of the steering axis Csr and the rear wheel 203 rin the basic posture state is set, as stated above, such that the heighta′ of the intersection point Er′ from the ground surface 110 is lowerthan the ground surface 110, for the following reason.

According to various experiments and studies conducted by the presentinventors, in order to cause a moment (in the roll direction) effectivein stably controlling the posture of the vehicle body 202 to act on thevehicle body 202 by the steering of the rear wheel 203 r of thetwo-wheeled vehicle 201A, it is preferable that the height a′ of theaforesaid intersection point Er′ from the ground surface 110 is lowerthan a certain level (including the case where it is lower than theground surface 110).

In view of the foregoing, in the present embodiment, the relativearrangement of the steering axis Csr and the rear wheel 203 r in thebasic posture state has been set as described above, by way of example,such that the rear wheel 203 r of the two-wheeled vehicle 201A has anegative trail. The trail of the rear wheel 203 r of the two-wheeledvehicle 201A, however, does not necessarily have to be negative; therelative arrangement of the steering axis Csr and the rear wheel 203 rmay be set such that the rear wheel 203 r has a positive trail.Basically, what is required is only that the steering of the rear wheel203 r can cause a moment in the roll direction to act on the vehiclebody 202.

The aforesaid actuator 208 generates, as a steering force for performingthe steering of the rear wheel 203 r, a rotative driving force to causethe rear wheel 203 r to rotate about the steering axis Csr. In thepresent embodiment, this actuator 208 is made up of an electric motor(with a speed reducer). The actuator 208 (hereinafter, also referred toas “rear-wheel steering actuator 208”) is connected to the rear-wheelsupport mechanism 205 so as to apply the rotative driving force aboutthe steering axis Csr to the rear-wheel support mechanism 205.

Accordingly, as the rotative driving force is applied from therear-wheel steering actuator 208 to the rear-wheel support mechanism205, the rear-wheel support mechanism 205 is rotatively driven about thesteering axis Csr together with the rear wheel 203 r. As a result, therear wheel 203 r is steered by the rotative driving force from therear-wheel steering actuator 208.

It should be noted that the actuator 208 is not limited to the electricmotor; it may be made up, for example, of a hydraulic actuator.

Besides the above-described mechanical configuration, the two-wheeledvehicle 201A includes, as shown in FIG. 15, a control device 215 whichcarries out control processing for controlling the operations of therear-wheel steering actuator 208 and rear-wheel driving actuator 209(and, hence, controlling the posture of the vehicle body 202 and so on).

The two-wheeled vehicle 201A further includes, as sensors for detectingvarious kinds of state quantities necessary for the control processingin the control device 215, a vehicle-body inclination detector 216 fordetecting an inclination angle φb in the roll direction of the vehiclebody 202, a rear-wheel steering angle detector 217 for detecting asteering angle δr (angle of rotation about the steering axis Csr) of therear wheel 203 r, a rear-wheel rotational speed detector 218 fordetecting a rotational speed (angular velocity) of the rear wheel 203 r,and an accelerator manipulation detector 219 which outputs a detectionsignal corresponding to the manipulated variable (rotational amount) ofthe accelerator grip of the operation apparatus 207.

It should be noted that the steering angle δr of the rear wheel 203 rmore specifically means the rotational angle of the rear wheel 203 rfrom the steering angle (neutral steering angle) in its non-steeredstate (the state in which the direction of the axle centerline of therear wheel 203 r is orthogonal to the longitudinal direction of thevehicle body 202). Therefore, the steering angle δr of the rear wheel203 r in the non-steered state is “0”.

The positive rotational direction of the steering angle δr of the rearwheel 203 r corresponds to the direction of rotation that makes thefront end of the rear wheel 203 r turn left with respect to the vehiclebody 202 (in other words, the direction in which the rear wheel 203 rturns counterclockwise about the steering axis Csr as the two-wheeledvehicle 201A is seen from above).

The control device 215, which is an electronic circuit unit made up of aCPU, RAM, ROM, interface circuit and so on, is mounted on the vehiclebody 202. This control device 215 is configured to receive outputs(detection signals) from the respective detectors 216 to 219 describedabove.

The control device 215 may include a plurality of CPUs or processors.Further, the control device 215 may be made up of a plurality ofmutually communicable electronic circuit units.

The vehicle-body inclination detector 216, which is made up of anacceleration sensor and a gyro sensor (angular velocity sensor), forexample, is mounted on the vehicle body 202. In this case, the controldevice 215 carries out arithmetic processing on the basis of the outputsof the acceleration sensor and the gyro sensor to measure theinclination angle in the roll direction (more specifically, theinclination angle in the roll direction with respect to the verticaldirection (direction of gravitational force)) of the vehicle body 202.For this measurement, the technique proposed by the present applicant inJapanese Patent No. 4181113, for example, may be adopted.

The rear-wheel steering angle detector 217 is made up, for example, of arotary encoder attached to the rear-wheel steering actuator 208 on theaforesaid steering axis Csr.

The rear-wheel rotational speed detector 218 is made up, for example, ofa rotary encoder attached to the axle of the rear wheel 203 r.

The accelerator manipulation detector 219 is made up, for example, of arotary encoder or a potentiometer built in the operation apparatus 207.

The functions of the above-described control device 215 will bedescribed further with reference to FIG. 16. The XYZ coordinate systemused in the following description is, as shown in FIG. 14, a coordinatesystem in which, in the basic posture state of the two-wheeled vehicle201A, the vertical direction (up-and-down direction) is defined as theZ-axis direction, the longitudinal direction of the vehicle body 202 asthe X-axis direction, the lateral direction of the vehicle body 202 asthe Y-axis direction (Y-axis not shown in the figure), and a point onthe ground surface 110 immediately beneath the overall center of gravityG of the two-wheeled vehicle 201A as the origin.

Further, in the following description, as in the first embodiment, thesuffix “_act” is added to the reference characters of a state quantityas a sign indicating an actual value or its observed value (detectedvalue or estimate). For a desired value, the suffix “_cmd” is added.

The control device 215 includes, as functions implemented when the CPUexecutes installed programs (functions implemented by software) or asfunctions implemented by hardware, as shown in FIG. 16: an estimatedtraveling speed calculating section 233 which calculates an estimate ofthe actual value Vox_act (hereinafter, referred to as “estimatedtraveling speed Vox_act”) of the traveling speed Vox of the two-wheeledvehicle 201A, a desired posture state determining section 234 whichdetermines a desired value φb_cmd (hereinafter, referred to as “desiredroll angle φb_cmd”) of the roll angle (inclination angle in thedirection about the X axis (roll direction)) φb of the vehicle body 202and a desired value φb_dot_cmd (hereinafter, referred to as “desiredroll angular velocity φb_dot_cmd”) of the roll angular velocity φb_dotwhich is a temporal change rate of the roll angle φb, a control gaindetermining section 235 which determines values of a plurality of gainsK1, K2, K3, and K4 for posture control of the vehicle body 202, and adesired rear-wheel rotational transfer velocity determining section 236which determines a desired value Vr_cmd (hereinafter, referred to as“desired rear-wheel rotational transfer velocity Vr_cmd”) of therotational transfer velocity Vr of the rear wheel 203 r (translationalvelocity of the rear wheel 203 r as the rear wheel 203 r rolls on theground surface 110).

The control device 215 further includes a posture control arithmeticsection 237 which carries out arithmetic processing for the posturecontrol of the vehicle body 202 to thereby determine a desired valueδr_cmd (hereinafter, referred to as “desired rear-wheel steering angleδr_cmd”) of the steering angle δr of the rear wheel 203 r, a desiredvalue δr_dot_cmd (hereinafter, referred to as “desired rear-wheelsteering angular velocity δr_dot_cmd”) of the steering angular velocityδr_dot which is a temporal change rate of the steering angle δr, and adesired value δrdot2_cmd (hereinafter, referred to as “desiredrear-wheel steering angular acceleration δr_dot2_cmd”) of the steeringangular acceleration δr_dot2 which is a temporal change rate of thesteering angular velocity δr_dot.

The control device 215 carries out the processing in the above-describedfunctional sections successively at prescribed control processingcycles. The control device 215 then controls the rear-wheel steeringactuator 208 in accordance with the desired rear-wheel steering angleδr_cmd, the desired rear-wheel steering angular velocity δr_dot_cmd, andthe desired rear-wheel steering angular acceleration δr_dot2_cmddetermined by the posture control arithmetic section 237.

Further, the control device 215 controls the rear-wheel driving actuator209 in accordance with the desired rear-wheel rotational transfervelocity Vr_cmd determined by the desired rear-wheel rotational transfervelocity determining section 236.

The control processing performed by the control device 215 will bedescribed below in detail.

At each control processing cycle, the control device 215 first carriesout the processing in the estimated traveling speed calculating section233.

As shown in FIG. 16, the estimated traveling speed calculating section233 receives an estimate of the actual value Vr_act (hereinafter,referred to as “estimated rear-wheel rotational transfer velocityVr_act”) of the rotational transfer velocity Vr of the rear wheel 203 r(translational velocity of the rear wheel 203 r as the rear wheel 203 rrolls on the ground surface 110), and a detected value of the actualvalue δr_act (hereinafter, referred to as “detected rear-wheel steeringangle δr_act”) of the steering angle δr of the rear wheel 203 r, whichis indicated by an output from the rear-wheel steering angle detector217.

It should be noted that the estimated rear-wheel rotational transfervelocity Vr_act is a velocity which is calculated by multiplying adetected value (observed value) of the rotational angular velocity ofthe rear wheel 203 r, indicated by an output from the aforesaidrear-wheel rotational speed detector 218, by a predetermined effectiverolling radius of the rear wheel 203 r.

The estimated traveling speed calculating section 233 carries out theprocessing shown in the block diagram in FIG. 17 to calculate anestimated traveling speed Vox_act.

In FIG. 17, a processing section 233-1 is a processing section whichmultiplies a detected rear-wheel steering angle δr_act at the currenttime by a cosine value of the caster angle θcr of the rear wheel 203 r,to thereby calculate an estimate of the actual value δ′r_act(hereinafter, referred to as “estimated rear-wheel effective steeringangle δ′r_act”) of a rear-wheel effective steering angle δ′r whichcorresponds to the rotational angle in the yaw direction of the rearwheel 203 r.

Here, the rear-wheel effective steering angle δ′r is an angle of theline of intersection of the ground surface 110 and the rotational planeof the rear wheel 203 r being steered (plane passing through the centerof the axle of the rear wheel 203 r and orthogonal to the axlecenterline of the rear wheel 203 r) with respect to the longitudinaldirection (X-axis direction) of the vehicle body 202.

In the case where the roll angle φb of the vehicle body 202 isrelatively small, the estimated rear-wheel effective steering angleδ′r_act can be calculated approximately by the following expression(11). The processing in the above-described processing section 233-1 isthe processing of approximately calculating δ′r_act by the expression(11).

δ′r_act=cos(θcr)*δr_act  (11)

To further improve the accuracy of δ′r_act, δ′r_act may be obtained by amapping from δr_act. Alternatively, to still further improve theaccuracy of δ′r_act, δ′r_act may be obtained by a mapping(two-dimensional mapping) or the like from the detected rear-wheelsteering angle δr_act and a detected value of the actual roll angleφb_act of the vehicle body 202, which is indicated by an output from thevehicle-body inclination detector 216.

In FIG. 17, a processing section 233-2 represents a processing sectionwhich obtains a cosine value cos(δ′r_act) of the estimated rear-wheeleffective steering angle δ′r_act calculated in the processing section233-1, and a processing section 233-3 represents a processing sectionwhich multiplies an estimated rear-wheel rotational transfer velocityVr_act at the current time by the above-described cosine valuecos(δ′r_act) to thereby calculate an estimated traveling speed Vox_act.

Accordingly, the estimated traveling speed calculating section 233 isconfigured to calculate Vox_act by multiplying Vr_act by the cosinevalue cos(δ′r_act) of δ′r_act. That is, Vox_act is calculated by thefollowing expression (12).

$\begin{matrix}\begin{matrix}{{Vox\_ act} = {{Vr\_ act}*{\cos \left( {\delta^{\prime}{r\_ act}} \right)}}} \\{= {{Vr\_ act}*{\cos \left( {{\delta r\_ act}*{\cos \left( {\theta \; {cr}} \right)}} \right)}}}\end{matrix} & (12)\end{matrix}$

The estimated traveling speed Vox_act calculated in this mannercorresponds to a component in the X-axis direction of the estimatedrear-wheel rotational transfer velocity Vr_act.

It should be noted that in the processing in the estimated travelingspeed calculating section 233, the estimated traveling speed Vox_act maybe calculated by the aforesaid expression (2) explained in conjunctionwith the first embodiment.

Further, instead of the detected rear-wheel steering angle δr_act andthe estimated rear-wheel rotational transfer velocity Vr_act at thecurrent time, a value (last time's value) δr_cmd_p of the desiredrear-wheel steering angle δr_cmd, calculated by the posture controlarithmetic section 237 (described later) in the last time's controlprocessing cycle, and a value (last time's value) Vr_cmd_p of thedesired rear-wheel rotational transfer velocity Vr_cmd, calculated bythe desired rear-wheel rotational transfer velocity determining section236 (described later) in the last time's control processing cycle,respectively, may be used. More specifically, δr_cmd_p and Vr_cmd_p maybe used to perform computation similar to that in the right side of theabove expression (12), and the resultant value(=Vr_cmd_p*cos(δr_cmd_p*cos(θcr))) may be obtained as a pseudo estimate(alternative observed value) as an alternative to the estimatedtraveling speed Vox_act.

Further, in obtaining the pseudo estimate (alternative observed value)as an alternative to the estimated traveling speed Vox_act, δr_cmd_p maybe used instead of the detected rear-wheel steering angle δr_act at thecurrent time, and the estimated rear-wheel rotational transfer velocityVr_act may be used as it is. Conversely, Vr_cmd_p may be used instead ofthe estimated rear-wheel rotational transfer velocity Vr_act at thecurrent time, and the detected rear-wheel steering angle δr_act may beused as it is.

Next, the control device 215 carries out the processing in the desiredrear-wheel rotational transfer velocity determining section 236.

As shown in FIG. 16, the desired rear-wheel rotational transfer velocitydetermining section 236 receives a detected value of the actual value ofthe accelerator manipulated variable, which is indicated by an outputfrom the aforesaid accelerator manipulation detector 219.

The desired rear-wheel rotational transfer velocity determining section236 determines a desired rear-wheel rotational transfer velocity Vr_cmdby the processing shown in the block diagram in FIG. 19, i.e. theprocessing in a processing section 236-1.

The processing section 236-1 determines the desired rear-wheelrotational transfer velocity Vr_cmd from a detected value of theaccelerator manipulated variable at the current time, by a presetconversion function.

The conversion function is a function which is defined, for example, bya mapping or an arithmetic expression. This conversion function isbasically set such that Vr_cmd determined by the conversion functionincreases monotonically as the accelerator manipulated variableincreases.

The conversion function is set, for example, with the trend asillustrated by the graph in FIG. 19. In this case, the processingsection 236-1 determines Vr_cmd to be zero when the detected value ofthe accelerator manipulated variable falls within the dead band range(range near zero) from zero to a prescribed first acceleratormanipulated variable A1.

Further, when the detected value of the accelerator manipulated variablefalls within the range from the first accelerator manipulated variableA1 to a prescribed second accelerator manipulated variable A2 (>A1), theprocessing section 236-1 determines Vr_cmd such that Vr_cmd increasesmonotonically as the accelerator manipulated variable increases and thatthe rate of increase of Vr_cmd (increase of Vr_cmd_per unit increase ofthe accelerator manipulated variable) increases smoothly.

When the detected value of the accelerator manipulated variable fallswithin the range from the second accelerator manipulated variable A2 toa prescribed third accelerator manipulated variable A3 (>A2), theprocessing section 236-1 determines Vr_cmd such that Vr_cmd increasesmonotonically, at a constant rate of increase, as the acceleratormanipulated variable increases.

Further, when the detected value of the accelerator manipulated variableexceeds the third accelerator manipulated variable A3, the processingsection 236-1 determines Vr_cmd such that it remains at a constant value(at the value corresponding to A3).

Next, the control device 215 carries out the processing in the controlgain determining section 235. As shown in FIG. 16, the control gaindetermining section 235 receives, via a delay element 238, a last time'sdesired rear-wheel steering angle δr_cmd_p, which is a value (lasttime's value) of the desired rear-wheel steering angle δr_cmd determinedby the posture control arithmetic section 237 in the last time's controlprocessing cycle of the control device 215. The control gain determiningsection 235 also receives an estimated traveling speed Vox_actcalculated by the estimated traveling speed calculating section 233 inthe current time's control processing cycle.

The control gain determining section 235 carries out the processingshown in the block diagram in FIG. 18, for example, to determine valuesof a plurality of gains K1, K2, K3, and K4 for the posture control ofthe vehicle body 202.

The values of the gains K1, K2, K3, and K4 are each determined variablyin accordance with δr_cmd_p and Vox_act, or in accordance with Vox_act,as will be described in detail later.

Next, the control device 215 carries out the processing in the desiredposture state determining section 234. The desired posture statedetermining section 234 determines a desired roll angle φb_cmd and adesired roll angular velocity φb_dot_cmd of the vehicle body 202. In thepresent embodiment, the desired posture state determining section 234sets both of the desired roll angle φb_cmd and the desired roll angularvelocity φb_dot_cmd to zero, by way of example.

Next, the control device 215 carries out the processing in the posturecontrol arithmetic section 237. As shown in FIG. 16, the posture controlarithmetic section 237 receives the desired roll angle φb_cmd and thedesired roll angular velocity φb_dot_cmd determined by the desiredposture state determining section 234, a detected value φb_act(hereinafter, referred to as “detected roll angle φb_act”) of the actualroll angle and a detected value φb_dot_act (hereinafter, referred to as“detected roll angular velocity φb_dot_act”) of the actual roll angularvelocity, indicated by an output from the vehicle-body inclinationdetector 216, and the gains K1, K2, K3, and K4 determined by the controlgain determining section 235.

The posture control arithmetic section 237 uses the above-describedinput values to carry out the processing shown in the block diagram inFIG. 20, to thereby determine a desired rear-wheel steering angleδr_cmd, a desired rear-wheel steering angular velocity δr_dot_cmd, and adesired rear-wheel steering angular acceleration δr_dot2_cmd.

In FIG. 20, a processing section 237-1 represents a processing sectionwhich obtains a deviation of a detected roll angle φb_act from a desiredroll angle φb_cmd, a processing section 237-2 represents a processingsection which multiplies the output of the processing section 237-1 bythe gain K1, a processing section 237-3 represents a processing sectionwhich obtains a deviation of a detected roll angular velocity φb_dot_actfrom a desired roll angular velocity φb_dot_cmd, a processing section237-4 represents a processing section which multiplies the output of theprocessing section 237-3 by the gain K2, a processing section 237-5represents a processing section which multiplies a last time's desiredrear-wheel steering angle δr_cmd_p by the gain K3, a processing section237-6 represents a processing section which multiplies a last time'sdesired rear-wheel steering angular velocity δr_dot_cmd_p, which is avalue of the desired rear-wheel steering angular velocity δr_dot_cmddetermined by the posture control arithmetic section 237 in the lasttime's control processing cycle, by the gain K4, and a processingsection 237-7 represents a processing section which sums up the outputsfrom the processing sections 237-2 and 237-4 and the values, eachmultiplied by −1, of the outputs from the processing sections 237-5 and237-6, to thereby calculate a desired rear-wheel steering angularacceleration δr_dot2_cmd.

Further, a processing section 237-8 represents a processing sectionwhich integrates the output of the processing section 237-7 to obtain adesired rear-wheel steering angular velocity δr_dot_cmd, a processingsection 237-9 represents a delay element which outputs the output fromthe processing section 237-8 in the last time's control processing cycle(i.e. last time's desired rear-wheel steering angular velocityδr_dot_cmd_p) to the processing section 237-6, a processing section237-10 represents a processing section which integrates the output ofthe processing section 237-8 to obtain a desired rear-wheel steeringangle δr_cmd, and a processing section 237-11 represents a delay elementwhich outputs the output from the processing section 237-10 in the lasttime's control processing cycle (i.e. last time's desired rear-wheelsteering angle δr_cmd_p) to the processing section 237-5.

Accordingly, the posture control arithmetic section 237 calculates thedesired rear-wheel steering angular acceleration δr_dot2_cmd by thefollowing expression (13).

$\begin{matrix}{{{\delta r\_ dot2}{\_ cmd}} = {{K\; 1*\left( {{\varphi b\_ cmd} - {\varphi b\_ act}} \right)} + {K\; 2*\left( {{{\varphi b\_ dot}{\_ cmd}} - {{\varphi b\_ dot}{\_ act}}} \right)} - {K\; 3*{\delta r\_ cmd}{\_ p}} - {K\; 4*{\delta r\_ dot}{\_ cmd}{\_ p}}}} & (13)\end{matrix}$

In the above expression (13), K1*(φb_cmd−φb_act) is a feedbackmanipulated variable having the function of making the deviation(φb_cmd−φb_act) approach “0”, K2*(φb_dot_cmd−φb_dot_act) is a feedbackmanipulated variable having the function of making the deviation(φb_dot_cmd−φb_dot_act) approach “0”, −K3*δr_cmd_p is a feedbackmanipulated variable having the function of making δr_cmd approach “0”,and

-   -   K4*δr_dot_cmd_p is a feedback manipulated variable having the        function of making δr_dot_cmd approach “0”.

The posture control arithmetic section 237 integrates δr_dot2_cmddetermined by the above expression (13) to determine a desiredrear-wheel steering angular velocity δr_dot_cmd. Further, the posturecontrol arithmetic section 237 integrates this δr_dot_cmd to determine adesired rear-wheel steering angle δr_cmd.

It should be noted that δr_cmd_p and δr_dot_cmd_p used in thecomputation of the expression (13) have the meanings as pseudo estimates(alternative observed values) of the actual steering angle and steeringangular velocity, respectively, of the rear wheel 203 r at the currenttime. Therefore, instead of δr_cmd_p, a detected rear-wheel steeringangle δr_act at the current time may be used. Further, instead ofδr_dot_cmd_p, a detected rear-wheel steering angular velocity δr_dot_act(detected value of the actual steering angular velocity of the rearwheel 203 r) based on an output from the aforesaid rear-wheel steeringangle detector 217 may be used.

The above has described the processing in the posture control arithmeticsection 237.

In accordance with the processing in the posture control arithmeticsection 237, the desired rear-wheel steering angular accelerationδr_dot2_cmd is basically determined such that any divergence of theactual roll angle (detected roll angle φb_act) of the vehicle body 202of the two-wheeled vehicle 201A from a desired roll angle φb_cmd, or anydivergence of the actual roll angular velocity (detected roll angularvelocity φb_dot_act) of the vehicle body 202 of the two-wheeled vehicle201A from a desired roll angular velocity φb_dot_cmd, is eliminatedthrough manipulation of the steering angle δr of the rear wheel 203 r(and, hence, that the actual roll angle or roll angular velocity of thevehicle body 202 of the two-wheeled vehicle 201A is restored to thedesired roll angle or desired roll angular velocity).

Further, in the present embodiment, the desired rear-wheel steeringangle δr_cmd and the desired rear-wheel steering angular velocityδr_dot_cmd are both “0”. Therefore, in the state where the actual rollangle of the vehicle body 202 of the two-wheeled vehicle 201A is held ata value which coincides, or almost coincides, with the desired rollangle φb_cmd, the desired rear-wheel steering angular accelerationδr_dot2_cmd is determined so as to keep the actual steering angle of therear wheel 203 r at “0” or almost “0”.

Here, the gains K1 to K4 (feedback gains related to the respectivefeedback manipulated variables in the right side of the aforesaidexpression (13)) used for calculating δr_dot2_cmd by the computation ofthe expression (13) are determined in the aforesaid control gaindetermining section 235. The processing in the control gain determiningsection 235 will now be described in detail.

The control gain determining section 235 determines the values of thegains K1 to K4 from the received estimated traveling speed Vox_act andlast time's desired rear-wheel steering angle δr_cmd_p, by theprocessing shown in the block diagram in FIG. 18.

In FIG. 18, a processing section 235-1 is a processing section whichdetermines the gain K1 in accordance with Vox_act and δr_cmd_p, and aprocessing section 235-2 is a processing section which determines thegain K2 in accordance with Vox_act and δr_cmd_p.

In the present embodiment, the processing section 235-1 determines thegain K1 from Vox_act and δr_cmd_p, in accordance with a presettwo-dimensional mapping (conversion function of two variables).Similarly, the processing section 235-2 determines the gain K2 fromVox_act and δr_cmd_p, in accordance with a preset two-dimensionalmapping (conversion function of two variables).

In these two-dimensional mappings, the trend of the change in value ofthe gain K1 with respect to Vox_act and δr_cmd_p and the trend of thechange in value of the gain K2 with respect to Vox_act and δr_cmd_p areset substantially similar to each other.

Specifically, as illustrated by the graphs shown in the processingsections 235-1 and 235-2 in FIG. 18, the two-dimensional mappings in theprocessing sections 235-1 and 235-2 are each set such that the magnitudeof the gain K1, K2 determined by the two-dimensional mapping has thetrend of monotonically decreasing with increasing Vox_act when δr_cmd_pis fixed to a given value.

Accordingly, the gains K1 and K2 as the feedback gains related to thefeedback manipulated variables having the function of stabilizing theposture in the roll direction of the vehicle body 202 of the two-wheeledvehicle 201A (making the detected roll angle φb_act and the detectedroll angular velocity φb_dot_act converge respectively to φb_cmd andφb_dot_cmd) are determined such that the magnitudes of the gains K1 andK2 each become smaller as the actual traveling speed (estimatedtraveling speed Vox_act) of the two-wheeled vehicle 201A becomesgreater.

In other words, the gains K1 and K2 are determined such that thesteering force that the rear-wheel steering actuator 208 generates, inaccordance with a deviation of φb_act from φb_cmd or a deviation ofφb_dot_act from φb_dot_cmd, in the direction of eliminating thedeviation is reduced when the actual traveling speed (estimatedtraveling speed Vox_act) of the two-wheeled vehicle 201A is in ahigh-speed range, as compared to when it is in a low-speed range.

Further, the two-dimensional mappings in the processing sections 235-1and 235-2 are each set such that the gain K1, K2 determined by themapping has the trend of monotonically decreasing with increasingmagnitude (absolute value) of δr_cmd_p when Vox_act is fixed to a givenvalue.

Accordingly, the gains K1 and K2 as the gains related to the feedbackmanipulated variables having the function of stabilizing the posture inthe roll direction of the vehicle body 202 of the two-wheeled vehicle201A are determined such that the magnitudes of the gains K1 and K2 eachbecome smaller as the magnitude of δr_cmd_p, corresponding to the actualsteering angle of the rear wheel 203 r, becomes larger.

Here, in the case where the magnitude of the actual steering angle ofthe rear wheel 203 r is large, compared to the case where it is small,the radius of curvature of the ground contact part of the steered wheel(rear wheel 203 r) as seen in a cross section including the groundcontact point of the steered wheel (rear wheel 203 r) and having anormal in the X-axis direction (longitudinal direction of the vehiclebody 202) becomes larger. Consequently, in the case where the magnitudeof the actual steering angle of the rear wheel 203 r is large, comparedto the case where it is small, the change in movement amount of theground contact point of the rear wheel 203 r according to the change inthe steering angle becomes larger.

Because of this, if the magnitudes of the gains K1 and K2 are setindependently of the actual steering angle, oscillation is likely tooccur in the control of the posture in the roll direction of the vehiclebody 202 of the two-wheeled vehicle 201A when the actual steering angleis large.

In view of the foregoing, in the present embodiment, it has beenconfigured such that the magnitudes of the gains K1 and K2 are changedin accordance with the magnitude of δr_cmd_p, as described above. Thiscan prevent the above-described oscillation even in the case where themagnitude (absolute value) of the actual steering angle of the rearwheel 203 r is large.

Further, in the block diagram in FIG. 18, a processing section 235-3 isa processing section which determines the gain K3 in accordance withVox_act, and a processing section 235-4 is a processing section whichdetermines the gain K4 in accordance with Vox_act.

In the present embodiment, the processing sections 235-3 and 235-4determine the gains K3 and K4, respectively, from Vox_act, in accordancewith conversion functions defined by preset mappings (or arithmeticexpressions).

These conversion functions are set, as illustrated by the graphs shownin the processing sections 235-3 and 235-4 in FIG. 18, such thatbasically the gains K3 and K4 each increase monotonically, between aprescribed upper limit and a prescribed lower limit, as Vox_actincreases.

In this case, in the conversion functions in the processing sections235-3 and 235-4, in the region where Vox_act takes a value near “0”, K3and K4 are each maintained at the lower limit. In the region whereVox_act takes a sufficiently large value, K3 and K4 are each maintainedat the upper limit.

As the gains K3 and K4 are determined in the above-described manner, thegains K3 and K4 as the feedback gains related to the feedbackmanipulated variables having the function of making the steering angleδr of the rear wheel 203 r approach zero are determined such that themagnitudes of the gains K3 and K4 become relatively large in the casewhere the actual traveling speed (estimated traveling speed Vox_act) ofthe two-wheeled vehicle 201A is relatively high (in a high-speed range),compared to the case where the actual traveling speed of the two-wheeledvehicle 201A is relatively low (in a low-speed range (including “0”)).

In the present embodiment, as the gains K1 and K3 are set as describedabove, the ratio between the gain K1, with a fixed steering angle of therear wheel 203 r, and the gain K3 (=K1/K3) is set such that the ratiobecomes smaller as the traveling speed of the two-wheeled vehicle 201Abecomes greater.

Similarly, as the gains K2 and K4 are set as described above, the ratiobetween the gain K2, with a fixed steering angle of the rear wheel 203r, and the gain K4 (=K2/K4) is set such that the ratio becomes smalleras the traveling speed of the two-wheeled vehicle 201A becomes greater.

Therefore, as the traveling speed of the two-wheeled vehicle 201Abecomes greater, the gains K1 and K2 as the feedback gains related tothe feedback manipulated variables having the function of controllingthe posture in the roll direction of the vehicle body 202 each becomerelatively small compared to the gains K3 and K4 as the feedback gainsrelated to the feedback manipulated variables having the function ofmaking the actual steering angle of the rear wheel 203 r converge tozero.

Accordingly, in the case where the actual traveling speed (estimatedtraveling speed Vox_act) of the two-wheeled vehicle 201A is relativelyhigh, i.e. in the state where the stability of the posture in the rolldirection of the vehicle body 202 is high, a rider of the two-wheeledvehicle 201A can readily change the posture in the roll direction (rollangle φb) of the vehicle body 202 by shifting the weight of the rider'sbody and so on, as in the case of a conventional two-wheeled vehicle(which is not provided with the function of controlling the posture inthe roll direction of the vehicle body).

It should be noted that the two-dimensional mappings for determining thegains K1 and K2 may each be set such that the value of K1, K2 isdetermined to be “0” or almost “0” when the estimated traveling speedVox_act reaches a certain level (i.e. when Vox_act is not lower than aprescribed speed).

With this configuration, the function of controlling the posture in theroll direction of the vehicle body 202 becomes substantially OFF whenthe actual traveling speed (estimated traveling speed Vox_act) of thetwo-wheeled vehicle 201A is relatively high. This can make thebehavioral characteristics of the two-wheeled vehicle 201A approach thecharacteristics comparable to those of a conventional two-wheeledvehicle in the case where the actual traveling speed of the two-wheeledvehicle 201A is high.

The above has described the details of the processing in the controlgain determining section 235 according to the present embodiment.

It should be noted that the gain K3 may be set such that, instead ofincreasing monotonically, it remains constant or decreasesmonotonically, between a prescribed upper limit and a prescribed lowerlimit, as Vox_act increases. In this case as well, the ratio between thegain K1, with a fixed steering angle of the rear wheel 203 r, and thegain K3 (=K1/K3) is set such that the ratio becomes smaller as thetraveling speed of the two-wheeled vehicle 201A becomes greater.

Similarly, the gain K4 may be set such that, instead of increasingmonotonically, it remains constant or decreases monotonically, between aprescribed upper limit and a prescribed lower limit, as Vox_actincreases. In this case as well, the ratio between the gain K2, with afixed steering angle of the rear wheel 203 r, and the gain K4 (=K2/K4)is set such that the ratio becomes smaller as the traveling speed of thetwo-wheeled vehicle 201A becomes greater.

Further, the gains K3 and K4 may be determined in accordance withVox_act and δr_cmd_p, as with the gains K1 and K2. For example, when apole placement method or the like is used to obtain rough approximationsof appropriate values for the set of gains K1 to K4 such that the ratiobetween the gain K1, with a fixed steering angle of the rear wheel 203r, and the gain K3 (=K1/K3) becomes smaller as the traveling speed ofthe two-wheeled vehicle 201A becomes greater, the gains K3 and K4 alsotake values dependent on δr_cmd_p. Therefore, the gains K3 and K4 arealso preferably determined in accordance with Vox_act and δr_cmd_p, aswith the gains K1 and K2, so that the values approach the approximationsof the appropriate values obtained from the pole placement method or thelike.

Further, for the conversion functions for determining the gains K1 andK2, conversion functions in other forms may be adopted, as long as theycan determine the gains with the above-described trends with respect toVox_act and δr_cmd_p. The conversion functions may each be set in a formother than the two-dimensional mapping (for example, one-dimensionalmapping and arithmetic expression may be combined). The same applies tothe case where the gains K3 and K4 are each determined by a conversionfunction in accordance with Vox_act and δr_cmd_p, or by a conversionfunction in accordance with Vox_act.

The last time's desired rear-wheel steering angle δr_cmd_p has themeaning as a pseudo estimate (alternative observed value) of the actualsteering angle of the rear wheel 203 r at the current time.

Accordingly, for determining the respective gains K1, K2, K3, and K4,the aforesaid detected rear-wheel steering angle δr_act may be usedinstead of δr_cmd_p.

Further, in the case where the response of the rear-wheel drivingactuator 209 is sufficiently quick, the value of the traveling speed(=Vr_cmd_p*cos(δr_cmd_p*cos(θcr)), hereinafter referred to as “lasttime's desired traveling speed Vox_cmd_p”) calculated by the computationsimilar to that in the aforesaid expression (12) from theabove-described last time's desired rear-wheel steering angle δr_cmd_pand a last time's desired rear-wheel rotational transfer velocityVr_cmd_p (desired rear-wheel rotational transfer velocity Vr_cmddetermined by the desired rear-wheel rotational transfer velocitydetermining section 236 in the last time's control processing cycle) hasthe meaning as a pseudo estimate (alternative observed value) of theactual traveling speed of the two-wheeled vehicle 201A at the currenttime.

Accordingly, for determining the respective gains K1, K2, K3, and K4,the above-described last time's desired traveling speed Vox_cmd_p may beused instead of Vox_act.

Controls of the aforesaid rear-wheel steering actuator 208 andrear-wheel driving actuator 209 will now be described.

The control device 215 further includes, as functions other than thefunctions shown in FIG. 16, a rear-wheel steering actuator controlsection 241 shown in FIG. 21 and a rear-wheel driving actuator controlsection 242 shown in FIG. 22.

The rear-wheel steering actuator control section 241 carries out drivecontrol of the rear-wheel steering actuator 208, by the controlprocessing shown in the block diagram in FIG. 21, for example, to causethe actual steering angle (detected rear-wheel steering angle δr_act) ofthe rear wheel 203 r to track a desired rear-wheel steering angleδr_cmd.

In this example, the rear-wheel steering actuator control section 241receives a desired rear-wheel steering angle δr_cmd, a desiredrear-wheel steering angular velocity δr_dot_cmd, and a desiredrear-wheel steering angular acceleration δr_dot2_cmd determined in theabove-described manner in the posture control arithmetic section 237, adetected rear-wheel steering angle δr_act, and a detected rear-wheelsteering angular velocity δr_dot_act which is a detected value of theactual steering angular velocity of the rear wheel 203 r.

It should be noted that the detected rear-wheel steering angularvelocity δr_dot_act is a value of the steering angular velocity which isrecognized on the basis of an output from the rear-wheel steering angledetector 217, or a value obtained by calculating a temporal change rateof the detected rear-wheel steering angle δr_act.

The rear-wheel steering actuator control section 241 performs theprocessing in an electric current command value determining section241-1 to determine, from the above-described input values, an electriccurrent command value I_δr_cmd which is a desired value of the electriccurrent passed through the rear-wheel steering actuator 208 (electricmotor).

This electric current command value determining section 241-1 determinesthe electric current command value I_δr_cmd by summing up a feedbackmanipulated variable component obtained by multiplying a deviation ofδr_act from δr_cmd by a gain Kδr_p of a prescribed value, a feedbackmanipulated variable component obtained by multiplying a deviation ofδr_dot_act from δr_dot_cmd by a gain Kδr_v of a prescribed value, and afeedforward manipulated variable component obtained by multiplyingδr_dot2_cmd by a gain Kδr_a of a prescribed value, as shown by thefollowing expression (14).

$\begin{matrix}{{{I\_\delta r}{\_ cmd}} = {{{K\delta r\_ p}*\left( {{\delta r\_ cmd} - {\delta r\_ act}} \right)} + {{K\delta r\_ v}*\left( {{{\delta r\_ dot}{\_ cmd}} - {{\delta r\_ dot}{\_ act}}} \right)} + {{K\delta r\_ a}*{\delta r\_ dot2}{\_ cmd}}}} & (14)\end{matrix}$

The rear-wheel steering actuator control section 241 then controls theactual electric current passed through the rear-wheel steering actuator208 (electric motor) to match the electric current command valueI_δr_cmd, by an electric current control section 241-2 which is made upof a motor driver or the like.

In this manner, the control is performed such that the actual steeringangle of the rear wheel 203 r tracks the desired rear-wheel steeringangle δr_cmd. In this case, the electric current command value I_δr_cmdincludes the third term in the right side of the above expression (14),i.e. the feedforward manipulated variable component, ensuring improvedtracking in the above-described control.

It should be noted that the technique of controlling the rear-wheelsteering actuator 208 to cause the actual steering angle of the rearwheel 203 r to track the desired rear-wheel steering angle δr_cmd is notlimited to the above-described technique; other techniques may be usedas well. For example, various kinds of known servo control techniquesrelated to electric motors (feedback control techniques for causing theactual angle of rotation of the rotor of the electric motor to track adesired value) may be adopted.

The rear-wheel driving actuator control section 242 carries out drivecontrol of the rear-wheel driving actuator 209, by the controlprocessing shown in the block diagram in FIG. 22, for example, to causethe actual rotational transfer velocity of the rear wheel 203 r to tracka desired rear-wheel rotational transfer velocity Vr_cmd (or to causethe actual rotational angular velocity of the rear wheel 203 r to tracka desired rotational angular velocity corresponding to Vr_cmd).

In this example, the rear-wheel driving actuator control section 242receives a desired rear-wheel rotational transfer velocity Vr_cmddetermined in the above-described manner in the desired rear-wheelrotational transfer velocity determining section 236, and an estimatedrear-wheel rotational transfer velocity Vr_act.

The rear-wheel driving actuator control section 242 performs theprocessing in an electric current command value determining section242-1 to determine, from the above-described input values, an electriccurrent command value I_Vr_cmd which is a desired value of the electriccurrent passed through the rear-wheel driving actuator 209 (electricmotor).

This electric current command value determining section 242-1 determinesa feedback manipulated variable component obtained by multiplying adeviation of Vr_act from Vr_cmd by a gain KVr_v of a prescribed value,as the electric current command value I_Vr_cmd, as shown by thefollowing expression (15).

I _(—) Vr_cmd=KVr _(—) v*(Vr_cmd−Vr_act)  (15)

It should be noted that, instead of using the above expression (15),I_Vr_cmd may be determined by, for example, multiplying a deviation ofthe detected value of the actual rotational angular velocity of the rearwheel 203 r, which is indicated by an output from the rear-wheelrotational speed detector 218, from a value obtained by dividing Vr_cmdby the effective rolling radius of the rear wheel 203 r (i.e. a desiredvalue of the rotational angular velocity of the rear wheel 203 r) by again of a prescribed value.

The rear-wheel driving actuator control section 242 then controls theactual electric current passed through the rear-wheel driving actuator209 (electric motor) to match the electric current command valueI_Vr_cmd, by an electric current control section 242-2 which is made upof a motor driver or the like.

In this manner, the control is performed such that the actual rotationaltransfer velocity of the rear wheel 203 r tracks the desired rear-wheelrotational transfer velocity Vr_cmd (or such that the actual rotationalangular velocity tracks the desired value of the rotational angularvelocity corresponding to Vr_cmd).

It should be noted that the technique of controlling the rear-wheeldriving actuator 209 to cause the actual rotational transfer velocity ofthe rear wheel 203 r to track the desired rear-wheel rotational transfervelocity Vr_cmd is not limited to the above-described technique; othertechniques may be used as well. For example, various kinds of knownspeed control techniques related to electric motors (feedback controltechniques for causing the actual rotational angular velocity of therotor of the electric motor to track a desired value) may be adopted.

The above has described the details of the control processing in thecontrol device 215 according the present embodiment.

Here, the correspondence between the present embodiment and the presentinvention will be described. In the present embodiment, the rear wheel203 r corresponds to the steered wheel in the present invention, and therear-wheel steering actuator 208 (electric motor) corresponds to thesteering actuator in the present invention.

Further, in the example of the present embodiment, the first motionalstate quantity in the present invention (motional state quantity of theinclination angle in the roll direction (roll angle) of the vehicle body202) is made up of a value of the roll angle φb as it is and a rollangular velocity φb_dot which is a temporal change rate of the rollangle.

Further, in the example of the present embodiment, the second motionalstate quantity in the present invention (motional state quantity of thesteering angle of the steered wheel (rear wheel 203 r)) is made up of avalue of the steering angle δr, as it is, of the rear wheel 203 r and asteering angular velocity δr_dot which is a temporal change rate of thesteering angle.

In the present embodiment, the desired values (φb_cmd, φb_dot_cmd) ofthe roll angle φb and the roll angular velocity φb_dot constituting thefirst motional state quantity are each set to zero, and the desiredvalues of the steering angle δr and the steering angular velocity δr_dotconstituting the second motional state quantity are each set to zero.

In the processing in the posture control arithmetic section 237, adesired rear-wheel steering angular acceleration δr_dot2_cmd as anoperational target of the rear-wheel steering actuator 208 (steeringactuator) is determined, by a feedback control law, so as to cause adeviation of each of the detected roll angle φb_act, the detected rollangular velocity φb_dot_act, the last time's desired rear-wheel steeringangle δr_cmd_p, representing a pseudo estimate of the steering angle δr,and the last time's desired rear-wheel steering angular velocityδr_dot_cmd_p, representing a pseudo estimate of the steering angularvelocity δr_dot, from the corresponding desired value to converge tozero.

Further, the steering force of the rear-wheel steering actuator 208 iscontrolled by the aforesaid rear-wheel steering actuator control section241 such that the actual steering angle of the rear wheel 203 r tracks adesired rear-wheel steering angle δr_cmd which has been determined byperforming integration twice on the above-described δr_dot2_cmd.

In this manner, the rear-wheel steering actuator 208 is controlled so asto stabilize the first motional state quantity (motional state quantityof the inclination angle in the roll direction of the vehicle body 202)and the second motional state quantity (motional state quantity of thesteering angle of the steered wheel (rear wheel 203 r)) and, hence, tostabilize the posture (in the roll direction) of the vehicle body 202.

It should be noted that in the present embodiment, the desiredrear-wheel steering angular acceleration δr_dot2_cmd of the steeredwheel (rear wheel 203 r) corresponds to the reference quantity in thepresent invention.

Further, in the present embodiment, the aforesaid gain K1 corresponds tothe sensitivity Ra1 of the change in value of the reference quantity(δr_dot2_cmd) to the change in observed value (φb_act) of theinclination angle in the roll direction of the vehicle body 202, and theaforesaid gain K2 corresponds to the sensitivity Ra2 of the change invalue of the reference quantity (δr_dot2_cmd) to the change in observedvalue (φb_dot_act) of the temporal change rate of the inclination anglein the roll direction of the vehicle body 202.

Furthermore, the aforesaid gain K3 corresponds to the sensitivity Rb1 ofthe change in value of the reference quantity (δr_dot2_cmd) to thechange in observed value (δr_act) of the steering angle δr of thesteered wheel (rear wheel 203 r), and the aforesaid gain K4 correspondsto the sensitivity Rb2 of the change in value of the reference quantity(δr_dot2_cmd) to the change in observed value (δr_dot_act) of thetemporal change rate of the steering angle δr of the steered wheel (rearwheel 203 r).

In this case, as the gains K1, K2, K3, and K4 are determined with theabove-described trends with respect to the observed value (Vox_act) ofthe actual traveling speed of the two-wheeled vehicle 201A, the steeringforce of the rear-wheel steering actuator 208 is controlled such thatthe magnitude of the ratio K1/K3 between the gains K1 and K3,corresponding to the ratio Ra1/Rb1 between the above-describedsensitivities Ra1 and Rb1, becomes smaller as the magnitude of theobserved value (Vox_act) of the traveling speed of the two-wheeledvehicle 201A becomes larger. Further, the steering force of therear-wheel steering actuator 208 is controlled such that the magnitudeof the ratio K2/K4 between the gains K2 and K4, corresponding to theratio Ra2/Rb2 between the above-described sensitivities Ra2 and Rb2,becomes smaller as the magnitude of the observed value (Vox_act) of thetraveling speed of the two-wheeled vehicle 201A becomes larger.

Further, as the gains K1 and K2 are determined with the above-describedtrends with respect to the observed value (δr_act) of the steering angleof the steered wheel (rear wheel 203 r), the steering force of therear-wheel steering actuator 208 is controlled such that the magnitudesof the gains K1 and K2 corresponding respectively to the above-describedsensitivities Ra1 and Ra2 each become smaller as the magnitude of theobserved value (δr_act) of the steering angle of the steered wheel (rearwheel 203 r) from the non-steered state thereof becomes larger.

According to the present embodiment described above, when thetwo-wheeled vehicle 201A is stopped or traveling at a low speed, in thecase where the actual roll angle (detected roll angle φb_act) of thevehicle body 202 deviates from the desired roll angle φb_cmd (in otherwords, in the case where the actual posture of the vehicle body 202deviates from a desired posture satisfying φb_act=φb_cmd), the steeringof the rear wheel 203 r by the steering force of the rear-wheel steeringactuator 208 can cause a moment (in the roll direction) capable ofmaking the actual roll angle of the vehicle body 202 restored to thedesired roll angle φb_cmd to act on the vehicle body 202, without theneed for the rider to intentionally move the operation apparatus 207.

That is, it is possible to cause the moment in the roll direction forstabilizing the posture of the vehicle body 202 to act on the vehiclebody 202. With this moment, the actual roll angle of the vehicle body202 is restored to the desired roll angle φb_cmd.

Further, through calculation of the desired rear-wheel steering angularacceleration δr_dot2_cmd by the aforesaid expression (13), the desiredrear-wheel steering angular acceleration δr_dot2_cmd (operational targetof the rear-wheel steering actuator 208) is determined such that adeviation (φb_cmd−φb_act) of the detected roll angle φb_act,representing an observed value of the current actual roll angle, fromthe desired roll angle φb_cmd of the vehicle body 202, a deviation(φb_dot_cmd−φb_dot_act) of the detected roll angular velocityφb_dot_act, representing an observed value of the current actual rollangular velocity, from the desired roll angular velocity φb_dot_cmd ofthe vehicle body 202, the last time's desired rear-wheel steering angleδr_cmd_p, representing a pseudo estimate of the current actual steeringangle (from the neutral steering angle) of the rear wheel 203 r, and thelast time's desired rear-wheel steering angular velocity δr_dot_cmd_p,representing a pseudo estimate of the angular velocity of the currentactual steering angle of the rear wheel 203 r, each approach “0”.

Therefore, the steering angle of the rear wheel 203 r is controlled soas to cause the actual roll angle and roll angular velocity of thevehicle body 202 to converge to the respective desired values (zero inthe present embodiment), while preventing the actual steering angle ofthe rear wheel 203 r from diverging from the neutral steering angle(while causing the actual steering angle to ultimately converge to theneutral steering angle).

Accordingly, the posture of the vehicle body 202 can be stabilizedsmoothly, particularly when the two-wheeled vehicle 201A is stopped ortraveling at a low speed. Further, the two-wheeled vehicle 201A can bestarted smoothly with the vehicle body 202 in a stable posture.

Further, the gains K1 and K2, which are the feedback gains related tothe posture control in the roll direction of the vehicle body 202, andthe gains K3 and K4, which are the feedback gains related to the controlof the steering angle of the rear wheel 203 r, are variably determined,as described above, in accordance with the estimated traveling speedVox_act, which is an observed value of the current actual travelingspeed (transfer velocity in the X-axis direction) of the two-wheeledvehicle 201A.

Accordingly, when the two-wheeled vehicle 201A is stopped or travelingat a low speed, it is possible to perform the steering of the rear wheel203 r to cause the actual roll angle of the vehicle body 202 to quicklyapproach the desired roll angle φb_cmd.

In the state where the two-wheeled vehicle 201A is traveling at a highspeed, even if the vehicle body 202 is leaned, the steering control ofthe rear wheel 203 r for causing the actual roll angle of the vehiclebody 202 to approach the desired roll angle φb_cmd is not performed, orsuch steering control is restricted. Consequently, a rider can readilyturn the two-wheeled vehicle 201A by banking the vehicle body 202 byshifting the weight of the rider's body, as with a conventionaltwo-wheeled vehicle.

Furthermore, the gains K1 and K2 are not only determined variably inaccordance with the estimated traveling speed Vox_act, but alsodetermined variably in accordance with the last time's desiredrear-wheel steering angle δr_cmd_p, representing a pseudo estimate ofthe current actual steering angle of the rear wheel 203 r, as describedabove. Accordingly, good posture control of the vehicle body 202 can beachieved with high robustness over a wide steering range of the rearwheel 203 r, without causing oscillation in the posture control of thevehicle body 202.

[Modifications]

Several modifications each related to the aforesaid first or secondembodiment will be described below.

In each of the aforesaid embodiments, in the posture control arithmeticsection 37 or 237, desired values of the steering angle, steeringangular velocity, and steering angular acceleration of the steered wheelmay be determined by performing, for example, the following processing.

In the processing in the posture control arithmetic section 37 in thecase of steering the front wheel 3 f, first, the value output from theaforesaid processing section 37-12 as a result of the processingidentical to that in the block diagram in FIG. 7 or 8 is obtained as aprovisional value δf′_cmd of the desired front-wheel steering angle, asshown in FIG. 23.

It should be noted that, in FIG. 23, the processing shown within thetwo-dot chain line frame (processing for calculating the provisionalvalue δf′_cmd) is identical to the processing in the block diagram inFIG. 8, although it may be identical to the processing in the blockdiagram in FIG. 7.

From this provisional value δf′_cmd, a desired front-wheel steeringangle δf_cmd is determined by the processing in a processing section37-15. In the processing in this processing section 37-15, theprovisional value δf′_cmd as an input value is converted into a desiredfront-wheel steering angle δf_cmd as an output value, by a conversionfunction having saturation characteristics (characteristics that theoutput value is saturated with respect to the input value) asillustrated by the graph in the figure. The conversion function isdefined by a mapping or an arithmetic expression.

The desired front-wheel steering angle δf_cmd determined in theprocessing section 37-15 is differentiated in a processing section37-16, whereby a desired front-wheel steering angular velocityδf_dot_cmd is determined. Further, the desired front-wheel steeringangular velocity δf_dot_cmd is differentiated in a processing section37-17, whereby a desired front-wheel steering angular accelerationδf_dot2_cmd is determined.

The same applies to the processing in the posture control arithmeticsection 237 in the case of steering the rear wheel 203 r. In this case,a provisional value δr′_cmd of the desired rear-wheel steering angle maybe calculated by the processing which corresponds to the processingshown within the two-dot chain line frame in FIG. 23 replaced with theprocessing in the block diagram in FIG. 20. Further, from thisprovisional value δr′_cmd, a desired rear-wheel steering angle δr_cmd, adesired rear-wheel steering angular velocity δr_dot_cmd, and a desiredrear-wheel steering angular acceleration δr_dot2_cmd may be determinedby the processes similar to those in the respective processing sections37-15, 37-16, and 37-17 in FIG. 23.

In the case where desired values of the steering angle, steering angularvelocity, and steering angular acceleration of the steered wheel (frontwheel 3 f or rear wheel 203 r) are determined by the processing in theposture control arithmetic section 37 or 237 in the above-describedmanner, in the processing in the control gain determining section 35 or235, the aforesaid gains K1 and K2 may be set independently of thesteering angle of the steered wheel.

In this manner as well, it is possible to control the steering actuator8 or 208 such that the sensitivity (the aforesaid sensitivity Ra1) ofthe change in value of the steering angular acceleration (δf_dot2_cmd orδr_dot2_cmd) to the change in observed value (φb_act) of the inclinationangle in the roll direction of the vehicle body 2 or 202 and thesensitivity (the aforesaid sensitivity Ra2) of the change in value ofthe steering angular acceleration Of dot2_cmd or δr_dot2_cmd) to thechange in observed value (φb_dot_act) of the temporal change rate of theinclination angle in the roll direction of the vehicle body 2 or 202both become smaller as the observed value of the steering angle of thesteered wheel becomes larger.

It should be noted that in each of the case of determining the desiredfront-wheel steering angle δf_cmd, the desired front-wheel steeringangular velocity δf_dot_cmd, and the desired front-wheel steeringangular acceleration δf_dot2_cmd in the posture control arithmeticsection 37 by the processing including the processes in theabove-described processing sections 37-15, 37-16, and 37-17 shown in theblock diagram in FIG. 23, and the case of determining the desiredrear-wheel steering angle δr_cmd, the desired rear-wheel steeringangular velocity δr_dot_cmd, and the desired rear-wheel steering angularacceleration δrdot2_cmd in the posture control arithmetic section 237 bythe processing including the processes similar to those in theabove-described processing sections 37-15, 37-16, and 37-17, the gainsK1 and K2 may be set such that they change with the trends similar tothose in each of the aforesaid embodiments in accordance with thesteering angle of the steered wheel (front wheel 3 f or rear wheel 203r).

In the first embodiment, the rear wheel 3 r is a non-steered wheel.

Alternatively, the rear wheel 3 r may be configured to be passivelysteered by, for example, the reaction force from the ground surface 110.

Further, in each of the aforesaid embodiments, as the motional statequantity of the inclination angle in the roll direction (roll angle) ofthe vehicle body 2, 202, which is a constituent element of thecontrolled state quantities, a value of roll angle φb and a roll angularvelocity φb_dot were used. Alternatively, the steering actuator(front-wheel steering actuator 8 or rear-wheel steering actuator 208)may be controlled, using the roll angle φb alone as the controlled statequantity related to the roll angle, to cause the state quantity toapproach a desired value.

Furthermore, as the motional state quantity of the steering angle of thesteered wheel, which is another constituent element of the controlledstate quantities, a value of the steering angle (δf or δr) and itsangular velocity Of dot or δr_dot) were used. Alternatively, thesteering actuator (front-wheel steering actuator 8 or rear-wheelsteering actuator 208) may be controlled, using the value of thesteering angle alone as the controlled state quantity related to thesteering angle of the steered wheel, to cause the state quantity toapproach a desired value.

The desired value of the motional state quantity of the inclinationangle in the roll direction (roll angle φb, roll angular velocityφb_dot) of the vehicle body 2, 202 may be set to a value other thanzero.

Further, the desired value of the motional state quantity of thesteering angle (steering angle δf or δr, steering angular velocityδf_dot or δr_dot) of the steered wheel may be set to a value other thanzero, as long as the value can stabilize the posture of the vehicle body2, 202.

The desired value of the motional state quantity of the inclinationangle in the roll direction (roll angle φb, roll angular velocityφb_dot) of the vehicle body 2, 202, or the desired value of the motionalstate quantity of the steering angle (steering angle δf or δr, steeringangular velocity δf_dot or δr_dot) of the steered wheel may be set to avalue that is determined in accordance with, for example, the forceapplied to the operation apparatus 7 (or 207) by the rider, or themanipulated variable of the operation apparatus 7 (or 207).

Further, in determining the desired value of the roll angle φb, thecentrifugal force during turning of the two-wheeled vehicle 1A or 201Amay be taken into account. That is, the desired value of the roll angleφb may be determined such that a moment generated about the origin ofthe XYZ coordinate system in the direction about the X axis (rolldirection) due to the gravitational force acting on the overall centerof gravity G of the two-wheeled vehicle 1A or 201A and a momentgenerated about the origin of the XYZ coordinate system in the directionabout the X axis (roll direction) due to the centrifugal force acting onthe overall center of gravity G are balanced (so that the sum of themoments becomes “0”).

In this case, the desired value of the roll angle φb (hereinafter,referred to as “desired roll angle φb_cmd”) can be determined, forexample, in the following manner. Hereinafter, the roll angle φb in thestate where the moments generated about the origin of the XYZ coordinatesystem due to the gravitational force and the centrifugal force actingon the overall center of gravity G are balanced with each other will becalled a “balanced roll angle φb_lean”.

This balanced roll angle φb_lean is obtained approximately by thefollowing expression (21).

φb_lean=−Vox_act*ωz_act/g  (21)

Here, ωz_act represents a turning angular velocity about the verticalaxis (yaw rate) of the vehicle body 2 or 202. For this value, forexample, a detected value of the yaw rate, which is indicated by anoutput from the aforesaid vehicle-body inclination detector 16 or 216including the angular velocity sensor, may be used.

Alternatively, ωz_act may be obtained from, for example, an actual valueof the aforesaid front-wheel effective steering angle δ′f (estimatedfront-wheel effective steering angle δ′f_act), an actual value of therear-wheel effective steering angle δ′r (estimated rear-wheel effectivesteering angle δ′r_act), and an actual value of the traveling speed Vox(estimated traveling speed Vox_act) of the two-wheeled vehicle 1A or201A, by the following expression (22).

ωz_act=Vox_act*((1/L)*tan(δ′f_act)−(1/L)*tan(δ′r_act))  (22)

In the case where the rear wheel 203 r is a non-steered wheel, as in theaforesaid first embodiment, the computation of the expression (22) canbe performed by setting: δ′r_act=0.

The balanced roll angle φb_lean calculated in the above-described mannermay be determined as the desired roll angle φb_cmd. Alternatively, avalue obtained by multiplying φb_lean by a positive constant of 1 orless may be determined as the desired roll angle φb_cmd.

The desired roll angle φb_cmd may be “0” when the two-wheeled vehicle 1Aor 201A is stopped before it starts moving, or when the traveling speedVox of the vehicle is sufficiently low.

Further, the desired value of the roll angular velocity φb_dot may beset to zero, although it may be set to a value other than zero as longas the value can stabilize the posture of the vehicle body 2, 202.

For example, the desired value of the roll angular velocity φb_dot maybe determined in accordance with the force applied to the operationapparatus 7 (or 207) by the rider or the manipulated variable of theoperation apparatus 7 (or 207).

In each of the aforesaid embodiments, in the processing in the posturecontrol arithmetic section 37 or 237, the desired front-wheel steeringangular acceleration δf_dot2_cmd or desired rear-wheel steering angularacceleration δr_dot2_cmd was determined as an operational target of thesteering actuator (front-wheel steering actuator 8 or rear-wheelsteering actuator 208).

In the processing in the posture control arithmetic section 37 in thefirst embodiment, however, a desired value of the torque about thesteering axis Csf of the steered wheel (front wheel 3 f) may bedetermined in place of, or in addition to, the desired front-wheelsteering angular acceleration δf_dot2_cmd. Then, in the aforesaidfront-wheel steering actuator control section 41, the steering force(torque) of the front-wheel steering actuator 8 may be controlled tocause the actual torque about the steering axis Csf to match the desiredvalue.

Similarly, in the processing in the posture control arithmetic section237 in the second embodiment, a desired value of the torque about thesteering axis Csr of the steered wheel (rear wheel 203 r) may bedetermined in place of, or in addition to, the desired rear-wheelsteering angular acceleration δr_dot2_cmd. Then, in the aforesaidrear-wheel steering actuator control section 241, the steering force(torque) of the rear-wheel steering actuator 208 may be controlled tocause the actual torque about the steering axis Csr to match the desiredvalue.

Furthermore, those equivalently transformed from the techniques, means,and algorithms shown in the above-described embodiments to produce thesame result can be regarded as being identical thereto.

What is claimed is:
 1. A mobile vehicle having a vehicle body and afront wheel and a rear wheel arranged spaced apart from each other in alongitudinal direction of the vehicle body, one of the front wheel andthe rear wheel being a steered wheel which can be steered about asteering axis tilted backward, the mobile vehicle comprising: a steeringactuator which generates a steering force for steering the steeredwheel; and a control device which controls the steering actuator,wherein the control device is configured to control the steeringactuator so as to stabilize controlled state quantities including afirst motional state quantity and a second motional state quantity, thefirst motional state quantity being a motional state quantity of aninclination angle in a roll direction of the vehicle body and includingat least a value of the inclination angle, the second motional statequantity being a motional state quantity of a steering angle of thesteered wheel and including at least a value of the steering angle, and,when a steering angular acceleration of the steered wheel steered by thesteering actuator or a torque about the steering axis applied to thesteered wheel from the steering actuator is defined as a referencequantity, the control device is configured to control the steeringactuator such that a magnitude of a ratio Ra1/Rb1 between sensitivityRa1 of a change in value of the reference quantity to a change inobserved value of the inclination angle in the roll direction of thevehicle body and sensitivity Rb1 of a change in value of the referencequantity to a change in observed value of the steering angle of thesteered wheel becomes smaller as a magnitude of an observed value of atraveling speed of the mobile vehicle becomes larger.
 2. The mobilevehicle according to claim 1, wherein the first motional state quantityincluded in the controlled state quantities is made up of a value of theinclination angle in the roll direction of the vehicle body and atemporal change rate of the inclination angle, the second motional statequantity included in the controlled state quantities is made up of avalue of the steering angle of the steered wheel and a temporal changerate of the steering angle, and the control device is configured tocontrol the steering actuator such that the magnitude of the ratioRa1/Rb1 becomes smaller as the magnitude of the observed value of thetraveling speed of the mobile vehicle becomes larger, and also such thatthe magnitude of a ratio Ra2/Rb2 between sensitivity Ra2 of the changein value of the reference quantity to the change in observed value ofthe temporal change rate of the inclination angle in the roll directionof the vehicle body and sensitivity Rb2 of the change in value of thereference quantity to the change in observed value of the temporalchange rate of the steering angle of the steered wheel becomes smalleras the magnitude of the observed value of the traveling speed of themobile vehicle becomes larger.
 3. The mobile vehicle according to claim1, wherein the control device is further configured to control thesteering actuator such that the magnitude of the sensitivity Ra1 of thechange in value of the reference quantity to the change in observedvalue of the inclination angle in the roll direction of the vehicle bodybecomes smaller as the magnitude of the observed value of the steeringangle of the steered wheel from a non-steered state thereof becomeslarger.
 4. The mobile vehicle according to claim 2, wherein the controldevice is further configured to control the steering actuator such thatthe magnitude of the sensitivity Ra1 of the change in value of thereference quantity to the change in observed value of the inclinationangle in the roll direction of the vehicle body and the magnitude of thesensitivity Ra2 of the change in value of the reference quantity to thechange in observed value of the temporal change rate of the inclinationangle each become smaller as the magnitude of the observed value of thesteering angle of the steered wheel from a non-steered state thereofbecomes larger.
 5. The mobile vehicle according to claim 1, furthercomprising an operation apparatus for a rider riding on the mobilevehicle to hold for performing steering of the steered wheel, theoperation apparatus being arranged to be rotatively driven by ahandlebar actuator for rotatively driving the operation apparatus inconjunction with the change of the steering angle of the steered wheelfrom a non-steered state thereof during the steering of the steeredwheel by the steering actuator, wherein the control device is furtherconfigured to control the handlebar actuator such that a rotationalamount of the operation apparatus has saturation characteristics withrespect to the steering angle of the steered wheel from the non-steeredstate thereof.